Surface Heat Production Research Articles

Radioelement abundances and heat production in the paleoarchaean and early neoarchaean granitoids of the Singhbhum Craton, eastern India: thermal and geodynamic implications

Summary Distributions of long-lived radioelements (Th, U, K) in the upper crust play a vital role in lithospheric thermal modeling and understanding of underlying geodynamic processes. In the present study, we report Th, U, K and radiogenic heat production (A) in Paleoarchaean and early Neoarchaean granitoids from the Singhbhum Craton, located in the eastern part of the Indian shield, for the first time in a systematic way, using laboratory gamma-ray spectrometric set-up. We have studied 204 samples consisting of Paleoarchaean gneiss, three phases of Paleoarchaean Singhbhum Granite and early Neoarchaean granitoid. Th, U, K and A in the Paleoarchaean Singhbhum Granite (10.8 ppm, 1.4 ppm, 2.4 per cent, and 1.3 μWm−3, N = 115) are found to be marginally higher than the Paleoarchaean gneiss (9.6 ppm, 1.7 ppm, 1.8 per cent, and 1.3 μWm−3, N = 74). In comparison, such values are much higher in the early Neoarchaean granitoid (31.1 ppm, 4.2 ppm, 3.9 per cent, and 3.6 μWm−3, N = 15). The surface heat production (1.36 μWm−3) of this craton is comparatively low compared to most cratons worldwide. In addition, it has the lowest average crustal heat production (0.42 µWm−3), due to which it will contribute little to the observed surface heat flow. Moreover, Th is a dominant component in heat production, followed by U and K in these granitoids. Spatially, radioelement ratios Th/U and K/U show similar trends as the radioelements, indicating systematic depletion of Th and U, compared to K. The study also indicates that the spatially separated coeval granitoids are formed from different magma sources in the heterogeneous crust that prevailed during the Archaeans. The lower radioelement abundances in the Paleoarchaean granitoids mostly resulted from the partial melting of mafic sources, whereas higher radioelement abundances in the early Neoarchaean granitoids resulted from the partial melting of the felsic source.

A Bootstrap-Based Tooth Surface Errors Statistics Methodology for Batch Hypoid Gears after Heat Treatment

In the manufacturing and production of hypoid gears, it is a necessary key problem to improve the tooth surface heat treatment precision and production efficiency of the hypoid gears. How to use advanced statistical theory and methods to evaluate the whole batch machining quality of the tooth surface after heat treatment is particularly urgent. In this connection, for the same batch of hypoid gears with the same gear material, numerical control gear milling method, and heat treatment specifications, a bootstrap-based statistics scheme of tooth surface errors after heat treatment is proposed in this paper. The bootstrap statistics model of the tooth surface errors for the batch hypoid gears is established. The bootstrap probability eigenvalues and confidence intervals of the measurement sequence points on the tooth surface errors are solved, and the optimizing selection of the single sampling numbers and the repeated sampling times is completed. On this basis, by applying the cubic NURBS surface fitting method, the mean value difference surface of the batch tooth surface errors data is constructed, the statistics laws of the whole batch tooth surface errors after heat treatment is determined, and the effective evaluation of the whole batch tooth surface accuracy is realized. Finally, the feasibility and correctness of the bootstrap-based statistics scheme are verified by the tooth surface errors bootstrap statistics application experiment of one kind of hypoid gear. The results show that with the help of the bootstrap statistics method proposed in this paper, it is not necessary to accurately measure the tooth surface errors of the whole batch of hypoid gears one by one. Only by randomly selecting 10 tooth surface samples and repeatedly sampling 2000 times, the original sample characteristic values of the whole batch tooth surface errors can be accurately estimated, and the heat treatment deformation statistics laws of the whole patch tooth surfaces can be also counted.

Spatio-temporal characterization of microbial heat production on undisturbed soil samples combining infrared thermography and zymography

Passive infrared thermography (IRT) has already been applied in several approaches for high-resolution and non-contact imaging of microbial hot spots and hot moments on soil sample surfaces. The technique has only been used on homogenized disturbed samples to characterize the in-situ heterogeneity of heat development. In this study, undisturbed top- and subsoils samples from two forest sites were used in a substrate-induced approach to capture surface heat production using passive IRT with homogeneously applied glucose and water. The soil sample surface temperature was measured at 10-minute intervals and a spatial resolution of 0.17 mm per pixel. The soil samples were incubated for five days during passive IRT measurements under controlled ambient conditions with a relative air humidity >95% and constant ambient air temperature of 20 °C. Soil sample surface characterization was done by using active IRT for soil moisture approximation and surface structure, digital photography to estimate soil organic carbon (SOC) contents from soil color parameters, and zymography to get an indicator of initial microbial activity. In a first step, surface temperature dynamics were characterized using mathematical and geostatistical methods concerning microbial hot spots and hot moments. The characterization of hot moments was performed using a Gaussian curve fit. The spatial information of the hot spots was described using geostatistical semivariance. In a second step, a stepwise forward regression using sample surface properties was performed to find explanatory variables for surface heat production. Finally, a hierarchical k-means clustering was applied to the sequential thermal images and transferred to the other spatial datasets for deeper insights into small-scale variations in heat production and to also consider the temporal perspective. With an ANOVA combined with Tukey’s HSD post hoc test, significant differences between the cluster groups were calculated. This study showed that the temperature difference between averaged glucose- and water-treated sample surface temperature increased up to 0.2 K with a maximum hot moment duration of nearly 46 h. The variance in the samples could not be mapped, since the maximum spatial variability of the sample surface temperature could not be represented in the sample sections. The regression analysis revealed significant influences by soil moisture content, approximated SOC content, as well as initial β-glucosidase activity in the subsoil, which could be confirmed by the k-means cluster analysis. There was an indication that soil brightness (SOC contents) was influencing heat production due to the varying soil-borne substrate availability. The initial β-glucosidase activity showed that the initial biotic state of the soil contributed to the temperature increase concerning the provision of energy for microbial activity. In conclusion, passive IRT is a helpful mapping tool for the spatio-temporal characterization of hot spots and hot moments. In this context, additional mapping techniques such as zymography help to gain insights into the process level of heat generation by microbial activity.

Thermal structure of the African continent based on magnetic data: Future geothermal renewable energy explorations in Africa

The defractal method was applied to the observed magnetic data and was used to estimate Curie point depth (CPD) i.e., depth to the base of magnetic sources (DBMS), near-surface geothermal gradient (GG), surface heat production and bulk crust thermal conductivity of Africa. A range of window sizes was tested using different values of the fractal parameter (α). The calculated DBMS ranges from 19 km to 112 km in Africa, and the GG varies from 15.9 °C/km to 30 °C/km (averaging 25 °C/km). Surface heat production values vary between 0.2 μW/m2 to 5.6 μW/m2, averaging 2.5 μW/m2. The calculated bulk crust thermal conductivity ranges from 1.4 W/mK to 3.4 W/mK with an average of 2.6 W/mK. In general, shallow DBMS, high GG, and high surface heat production coincide with known geothermal, volcanic, and seismic regions in Africa. Shallow DBMS, high GG, and high surface heat production were encountered in southeastern Africa, northeastern Africa (Egypt and Red Sea), and northern Africa (Hoggar region). High bulk crust thermal conductivity values are encountered in northern Africa (Algeria, Morocco, Libya), southeastern Africa and the East African Rift (EAR) regions.

An integrated approach to sustainable heat recovery in a sedimentary geothermal reservoir considering surface energy demands

Direct usage of low-to-medium enthalpy geothermal energy can provide clean and renewable energy for heating purposes. Optimum geothermal extraction strategies improve the efficiency and effectiveness supplying heat energy, which calls for a comprehensive and integrated study on geothermal reservoir development. In this paper, an integrated modeling workflow considering surface energy demands is presented to analyze the heat extraction process in a sedimentary geothermal reservoir. Effects of surface demands, well positioning, heat production rates, and number of geothermal wells on heat extraction efficiency are thoroughly studied. Results indicate that surface energy demands, well positioning, and heat production rates jointly decide the heat extraction effectiveness and the number of geothermal wells required. Neglecting surface energy demands decreases the effectiveness of heat extraction strategy planning. For the 27 surface energy demand cases studied in this work, the geothermal project can sustainably meet the surface demands in certain cases for up to 30 years, while in some cases, the project can only meet the surface demands for 4 years. In addition, the well spacing of 300m can maintain the heat production temperature at its initial level regardless of the heat production rates.

Estimating concentrations of heat producing elements in the crust near the Sudbury Neutrino Observatory, Ontario, Canada

Abstract Because the concentrations of uranium and thorium in the crust must be determined precisely for the future geoneutrino observations planned at the Sudbury Neutrino Observatory, we investigate whether airborne radiometric surveys can be used to constrain crustal radioactivity. The regional airborne surveys cover a wide area with high spatial resolution ( σ ) μW m − 3 for more than 176,000 values. The outcrop samples collected along a transect in the Superior Province yield an average heat production of 2.9 ± 2.4 ( σ ) μW m − 3 and core samples from drill holes yield an average of 2.5 ± 0.8 (σ) μW m − 3 . The high heat production in the rock samples is consistent with surface heat flux measurements near Sudbury with a mean value that is 12 mW m − 2 higher than the average Canadian Shield. The study shows that airborne aeromagnetic surveys give useful information on lateral variations in surface heat production but are unlikely to provide the reliable values of heat production needed to calculate the crustal geoneutrino flux. Crustal heat production will be best calculated from heat flux data complemented by heat production measurements on rock samples. The high mean heat production in Sudbury Igneous Complex samples (≈ 1.5 μW m − 3 ) suggests that the main source of the melt sheet was the very radioactive upper crust of the Superior Province or that the melt sheet was extremely enriched relative to a lower crustal source.

Bubbles in liquids with phase transition

In the forthcoming second part of this paper a system of balance laws for a multi-phase mixture with many dispersed bubbles in liquid is derived where phase transition is taken into account. The exchange terms for mass, momentum and energy explicitly depend on evolution laws for total mass, radius and temperature of single bubbles. Therefore in the current paper we consider a single bubble of vapor and inert gas surrounded by the corresponding liquid phase. The creation of bubbles, e.g. by nucleation is not taken into account. We study the behavior of this bubble due to condensation and evaporation at the interface. The aim is to find evolution laws for total mass, radius and temperature of the bubble, which should be as simple as possible but consider all relevant physical effects. Special attention is given to the effects of surface tension and heat production on the bubble dynamics as well as the propagation of acoustic elastic waves by including slight compressibility of the liquid phase. Separately we study the influence of the three phenomena heat conduction, elastic waves and phase transition on the evolution of the bubble. We find ordinary differential equations that describe the bubble dynamics. It turns out that the elastic waves in the liquid are of greatest importance to the dynamics of the bubble radius. The phase transition has a strong influence on the evolution of the temperature, in particular at the interface. Furthermore the phase transition leads to a drastic change of the water content in the bubble. It is shown that a rebounding bubble is only possible, if it contains in addition an inert gas. In Part 2 of the current paper the equations derived are sought in order to close the system of equations for multi-phase mixture balance laws for dispersed bubbles in liquids involving phase change.

Global heat flow trends resolved from multiple geological and geophysical proxies

Because global coverage of heat flow measurements is still poor in many areas, empirical estimators based on the geology, the thermotectonic age or the velocity structure of the upper mantle have often been used to affect an estimate to regions where such measurements are absent. On the basis of the assumption that heat flow is strongly related to its geodynamic environment, one may integrate multiple proxies derived from a large body of global geo- logical and geophysical data sets assembled during the past decades; these should help to better capture the variety of present-day settings. This idea is illustrated through two simple empirical methods: both of them are based on a set of examples, where heat flow measure- ments are associated with relevant terrestrial observables such as surface heat production, upper-mantle velocity structure, tectono-thermal age, on a 1◦ × 1◦ grid. To a given target point owning a number of observables, the methods associate a heat flow distribution rather than a deterministic value to account for intrinsic variability and uncertainty within a defined geodynamic environment. The 'best combination method' seeks the particular combination of observables that minimizes the dispersion of the heat flow distribution generated from the set of examples. The 'similarity method' attributes a weight to each example depending on its degree of similarity with the target point. The methods are transparent and are able to handle sets of observables that are not available over the whole Earth (e.g. heat production). The resulting trends of the mean heat flow deduced from the two methods do not differ strongly, but the similarity method shows a better accuracy in cross-validation tests. These tests suggest that the selected proxies have the potential to recover at least partly medium- to large-scale features of surface heat flow. The methods depict the main global trends of low heat flow in stable and ancient regions, and thermal high in active orogens and rift zones. Broad thermal anomalies are outlined in the Sahara and in the tectonically active eastern part of Antarctica. The similarity method estimates a continental heat loss of 13.6 ± 0.8 TW (2σ uncertainty), which is consistent with previous estimates.

Martian surface heat production and crustal heat flow from Mars Odyssey Gamma-Ray spectrometry

[1] Martian thermal state and evolution depend principally on the radiogenic heat-producing element (HPE) distributions in the planet's crust and mantle. The Gamma-Ray Spectrometer (GRS) on the 2001 Mars Odyssey spacecraft has mapped the surface abundances of HPEs across Mars. From these data, we produce the first models of global and regional surface heat production and crustal heat flow. As previous studies have suggested that the crust is a repository for approximately 50% of the radiogenic elements on Mars, these models provide important, directly measurable constraints on Martian heat generation. Our calculations show considerable geographic and temporal variations in crustal heat flow, and demonstrate the existence of anomalous heat flow provinces. We calculate a present day average surface heat production of 4.9 ± 0.3 × 10−11 W · kg−1. We also calculate the average crustal component of heat flow of 6.4 ± 0.4 mW · m−2. The crustal component of radiogenically produced heat flow ranges from <1 mW · m−2 in the Hellas Basin and Utopia Planitia regions to ∼13 mW · m−2 in the Sirenum Fossae region. These heat production and crustal heat flow values from geochemical measurements support previous heat flow estimates produced by different methodologies.

Constraints on the deep thermal structure of the Dharwar craton, India, from heat flow, shear wave velocities, and mantle xenoliths

[1] We have used constraints from seismic shear wave vertical velocity profiles, geothermobarometry estimates on mantle xenoliths, and surface heat flux and heat production measurements to analyze the thermal regime of the deep lithosphere beneath India. In the Dharwar craton of southern India, the shear wave velocity gradient in the mantle, as well as xenolith geothermobarometry data, suggests a low mantle heat flux, 14–20 mW m−2, consistent with surface heat flux measurements. However, for standard cratonic mantle composition, seismic velocities require Moho and mantle temperatures to be about 300 K higher than inferred from heat flux and xenolith data. This discrepancy can be only resolved by changing the mantle composition, specifically by increasing the Fe number. The shear wave velocities are highest beneath north central India, where calculated S wave travel times are 2 s shorter than in the Dharwar craton. These differences in traveltime and the very steep gradient in the shear wave velocity profiles in north central India cannot be explained by variations in mantle temperature but require differences in mantle composition.

Thermal regime of the lithosphere in the Canadian ShieldThis article is one of a series of papers published in this Special Issue on the themeLithoprobe — parameters, processes, and the evolution of a continent.

Geothermal studies were conducted within the framework of Lithoprobe to systematically document variations of heat flow and surface heat production in the major geological provinces of the Canadian Shield. One of the main conclusions is that in the Shield the variations in surface heat flow are dominated by the crustal heat generation. Horizontal variations in mantle heat flow are too small to be resolved by heat flow measurements. Different methods constrain the mantle heat flow to be in the range of 12–18 mW·m–2. Most of the heat flow anomalies (high and low) are due to variations in crustal composition and structure. The vertical distribution of radioelements is characterized by a differentiation index (DI) that measures the ratio of the surface to the average crustal heat generation in a province. Determination of mantle temperatures requires the knowledge of both the surface heat flow and DI. Mantle temperatures increase with an increase in surface heat flow but decrease with an increase in DI. Stabilization of the crust is achieved by crustal differentiation that results in decreasing temperatures in the lower crust. Present mantle temperatures inferred from xenolith studies and variations in mantle seismic P-wave velocity (Pn) from seismic refraction surveys are consistent with geotherms calculated from heat flow. These results emphasize that deep lithospheric temperatures do not always increase with an increase in the surface heat flow. The dense data coverage that has been achieved in the Canadian Shield allows some discrimination between temperature and composition effects on seismic velocities in the lithospheric mantle.

Lithospheric structure of the Canadian Shield inferred from inversion of surface-wave dispersion with thermodynamic a priori constraints

Abstract We argue for and present a reformulation of the seismic surface-wave inverse problem in terms of a thermal model of the upper mantle and apply the method to estimate lithospheric structure across much of the Canadian Shield. The reformulation is based on a steady-state temperature model, which we show to be justified for the studied region. The inverse problem is cast in terms of three thermal parameters: temperature in the uppermost mantle directly beneath Moho, mantle temperature gradient, and the potential temperature of the sublithospheric convecting mantle. In addition to the steady-state constraint, prior physical information on these model parameters is based on surface heat flow and heat production measurements, the condition that melting temperatures were not reached in the crust in Proterozoic times and other theoretical considerations. We present the results of a Monte Carlo inversion of surface-wave data with this ‘thermal parameterization’ subject to the physical constraints for upper mantle shear velocity and temperature, from which we also estimate lithospheric thickness and mantle heat flux. The Monte Carlo inversion gives an ensemble of models that fit the data, providing estimates of uncertainties in model parameters. We also estimate the effect of uncertainties in the interconversion between temperature and seismic velocity. Variations in lithospheric temperature and shear velocity are not well correlated with geological province or surface tectonic history. Mantle heat flow and lithospheric thickness are anti-correlated and vary across the studied region, from 11 mW/m 2 and nearly 400 km in the northwest to about 24 mW/m 2 and less than 150km in the southeast. The relation between lithospheric thickness and mantle heat flow is consistent with a power law relation similar to that proposed by Jaupart et al. (1998), who argued that the lithosphere and asthenosphere beneath the Canadian Shield are in thermal equilibrium and heat flux into the deep lithosphere is governed by small-scale sublithospheric convection.

Late Archaean to Palaeoproterozoic geotherms in the Kaapvaal craton, South Africa: constraints on the thermal evolution of the Witwatersrand Basin

ABSTRACTThe c. 2.97–2.71 Ga Witwatersrand Basin located in the Kaapvaal craton of South Africa represents a remnant of a large Late Archaean sedimentary basin that hosts the world's premier gold deposit within a series of conglomerate horizons. Evidence of postdepositional gold mobility within these conglomerates associated with hydrothermal–metamorphic activity has led to speculation about the Late Archaean to Palaeoproterozoic geothermal gradients in the basin. We use surface heat flow and heat production data from rocks in the basin and its environs in order to calculate detailed temperature profiles for the central Kaapvaal craton that show that the steady state crustal geotherm during the Late Archaean and Palaeoproterozoic was relatively cool at 15–20 K km−1. The geotherm in the upper crustal strata is also largely unaffected by substantial increases in the heat flow into the base of the crust. Consequently, regional greenschist facies metamorphism of the basin sediments could only have been achieved during a transient thermal event that advected heat into the upper crust. The most likely candidate for this is the Bushveld magmatic event at 2.06 Ga.

Geothermal modeling along a two-dimensional crustal profile in Southern Portugal

Crustal temperatures along a S–N trending profile crossing the main geological units of Southern Portugal, the South Portuguese Zone and the Ossa Morena Zone, were calculated by solving numerically the heat conduction equation in a 2-D geothermal model of the crust. Use of observed surface heat flow and heat production based on the empirical relationship between radiogenic heat sources and observed seismic velocities, yields temperatures at the crust/mantle boundary, which are higher than the upper limit (about 700 °C) of crustal temperatures based on magnetotelluric surveys. The most uncertain parameter of the model is the upper crust heat production, whose low value implies a large non-crustal component of surface heat flow, which must be conducted through the whole crust and increases the vertical temperature gradient. To overcome this uncertainty in heat sources, the Moho heat flow was estimated using Vitorello and Pollack’s [J. Geophys. Res. (1980) 983] estimate of the background heat flow of 27 mW m −2 arising from below the zone of crustal enrichment (identified in our model with the upper crust) and transient thermal perturbation, represented in Variscan units by 5–10 mW m −2. Taking into account the heat production of the middle and lower crust, the mean value of the Moho heat flow should be 28–33 mW m −2. The Moho heat flow was allowed to vary (with variation restricted to 0.2–1.0 mW m −2 per 5 km) around 28 or 33 mW m −2 along the profile in order to improve the fit between the calculated and measured surface heat flows. Because this approach yields a surface heat flow lower than observed, the residual differences were minimized by increasing the heat production of the upper crust, where the production was allowed to vary along the profile (with variation restricted to 0.02–0.2 μW m −3 per 5 km). If Moho heat flow is allowed to vary by a total of about 9–25 mW m −2, the upper crustal heat production necessary for the calculated surface heat flow to match the observed one is in the range 2–3 μW/m −3, which indicates a mostly granitic upper crust. The resulting Moho temperatures are below 700 °C everywhere along the profile in all model configurations considered.

Heat‐flow data in western Victoria

New heat‐flow data have been obtained in western Victoria at Horsham (89.8 ± 7.3 mW m‐2) and Warracknabeal (97.0 ± 8.7 mW m‐2). The results are significantly less than previous values obtained at Stawell and Castlemaine and consequently crustal models based on rapid cooling of high‐level melt emplacements require revision. More general models based on mid‐crustal detachments or underplating mechanisms do not require the preservation of a specific spatial anomaly and consequently remain unaffected. Previous inconsistencies between surface heat flow and surface heat production are eliminated if the new data are substituted for the previous Stawell and Castlemaine data.

Regional geochemistry and continental heat flow: implications for the origin of the South Australian heat flow anomaly

Existing measurements from South Australia define a broad (>250 km wide) zone of anomalously high surface heat flow (92±10 mW m −2). This zone is centred on the western margin of the Adelaide Fold Belt (Neoproterozoic to early Phanerozoic cover floored by Palaeoproterozoic to Mesoproterozoic basement), where it borders the eastern Gawler Craton and Stuart Shelf (Palaeoproterozoic–Mesoproterozoic). To the west, in the western Gawler Craton (Archaean to Palaeoproterozoic), heat flow averages ∼54 mW m −2 while to the east in the Willyama Inliers (Palaeoproterozoic) heat flow averages ∼75 mW m −2. We use a regional geochemical dataset comprising >2500 analyses to show that the anomalous heat flow zone correlates with exceptional surface heat production values, mainly hosted in Palaeoproterozoic to Mesoproterozoic granites. The median heat production of Precambrian ‘basement’ rocks increases from <3 μW m −3 west of the anomalous zone to ∼6 μW m −3 within the anomalous zone. In the highest known part of the heat flow anomaly, Mesoproterozoic gneisses and granites of the Mount Painter Province in the northern Adelaide Fold Belt yield an area-integrated mean heat production of 9.9 μW m −3. These data suggest that the anomalous heat flow reflects an unusual enrichment in U and Th in this part of the Proterozoic crust, with the total complement of these elements some 2–3 times greater than would be expected for Proterozoic crust on the basis of the global heat flow database. This extraordinary enrichment has played an important role in modulating the thermal regime of the crust in this region, and particularly its response to tectonic activity.

Heat flow in the Trans‐Hudson Orogen of the Canadian Shield: Implications for Proterozoic continental growth

Fourteen new heat flow and radiogenic heat production measurements have been obtained in the Paleo‐Proterozoic Trans‐Hudson Orogen of the Canadian Shield. This orogen, which consists of several distinctive belts, corresponds to a pulse of crustal growth through island arc magmatism between 1.9 and 1.8 Ga. The data now available include 17 previously published measurements. Heat flow variations that are related to the history of magmatism and internal differentiation of the belts provide constraints on the crustal assemblages in the different belts of the orogen. The average and standard deviation of heat flow values for the entire orogen, 42±11 mW m−2, are identical to those of the older Superior Province and of the younger Grenville Province. For the orogen as a whole, heat flow is weakly correlated to the heat production of surface rocks. High heat flow values are found in the Thompson belt, consisting of metasedimentary rocks deposited on the ancient continental margin of the Superior craton. There the accumulation of sediments derived from older and differentiated continental upper crust has resulted in significant concentrations of radioelements in large volumes of rocks. The heat flow is low in the belts that expose juvenile Proterozoic crust consisting mostly of arc‐related volcanic rocks. In the Flin Flon‐Snow Lake Belt, the average heat flow is the same as the average of the orogen. The low heat production and the lack of correlation between heat flow and heat production suggest that the supracrustal volcanics exposed at the surface are thin and rest on a basement richer in radioelements. In the Lynn Lake belt, the heat flow is significantly lower than the average for the orogen although the surface heat production is not low. The heat flow data require a thin (&lt;10 km) surface layer overlying the mid and lower crust depleted in radioelements. Around the town of Lynn Lake, heat flow is consistently low over a distance of ≈40 km. The coincidence between this “cold spot” and anomalously thick crust suggests that deep crustal roots may be preserved because of the stronger rheology implied by the low temperatures. The evolution of the Trans‐Hudson Orogen exemplifies the interplay between the processes generating rocks of evolved composition, which require crustal thickening, and those forming “normal” continental crust with average thickness, which require crustal flow and soft crustal rheology.

Petrology of Peridotite and Pyroxenite Xenoliths from the Jericho Kimberlite: Implications for the Thermal State of the Mantle beneath the Slave Craton, Northern Canada

We report comprehensive petrological and thermobarometric data for the following typesof mantle xenoliths from the Jericho kimberlite in the Slave craton: (1) coarse peridotite; (2) porphyroclastic peridotite; (3) megacrystalline pyroxenite; (4) ilmenite–garnet wehrlite and clinopyroxenite. The varieties of the upper-mantle xenoliths, and their proportions, petrography and mineralogy, mainly resemble those from kimberlites of other cratons. Unique characteristics of the north–central Slave mantle include the presence of high-temperature megacrystalline pyroxenite and an unusually high proportion of pyroxenitic magmatic rocks related in origin to megacrysts. Other unique aspects of Jerichoperidotitic mantle are: (1) a pronounced Cr enrichment in mineral chemistry within high-temperature peridotite; (2) an anomalously high proportion of chemically unequilibrated samples; (3) an uncommon pattern in silicate mineral chemistry in spinel-bearing peridotite that reflects equilibration with spinel. The central Slave mantle is colder than the mantle beneath the rest of the North American craton and the mantle beneath Kaapvaal and Siberian cratons. Thermobarometric data are fitted to a model steady-state geotherm with an exponential decrease in heat production with depth using a geologically constrained valueof surface heat production at Jericho. The estimated model values of surface heat flow (Q0 = 52–53 mW/m2) show an excellent agreement with two heat flow measurements available for the Slave craton (53–55 mW/m2). Thus, the cool upper mantle here coexists with a highly radiogenic crust.

Petrology of Peridotite and Pyroxenite Xenoliths from the Jericho Kimberlite: Implications for the Thermal State of the Mantle beneath the Slave Craton, Northern Canada

We report comprehensive petrological and thermobarometric data for the following typesof mantle xenoliths from the Jericho kimberlite in the Slave craton: (1) coarse peridotite; (2) porphyroclastic peridotite; (3) megacrystalline pyroxenite; (4) ilmenite–garnet wehrlite and clinopyroxenite. The varieties of the upper-mantle xenoliths, and their proportions, petrography and mineralogy, mainly resemble those from kimberlites of other cratons. Unique characteristics of the north–central Slave mantle include the presence of high-temperature megacrystalline pyroxenite and an unusually high proportion of pyroxenitic magmatic rocks related in origin to megacrysts. Other unique aspects of Jerichoperidotitic mantle are: (1) a pronounced Cr enrichment in mineral chemistry within high-temperature peridotite; (2) an anomalously high proportion of chemically unequilibrated samples; (3) an uncommon pattern in silicate mineral chemistry in spinel-bearing peridotite that reflects equilibration with spinel. The central Slave mantle is colder than the mantle beneath the rest of the North American craton and the mantle beneath Kaapvaal and Siberian cratons. Thermobarometric data are fitted to a model steady-state geotherm with an exponential decrease in heat production with depth using a geologically constrained valueof surface heat production at Jericho. The estimated model values of surface heat flow (Q0 = 52–53 mW/m2) show an excellent agreement with two heat flow measurements available for the Slave craton (53–55 mW/m2). Thus, the cool upper mantle here coexists with a highly radiogenic crust.

Modelling of the Thermal Parameters in Tobacco Curing

Analytical and numeric models have been created for writing surface heat-production and heat transmitting parameters equation gives a possibility for calculating some typical physical parameters.The model for thermal behaving of curing has some special requirements. Some trials have been done for numeric solving of our partial differencial equation. For examination of our model, laboratory measurements were carried out by infrared method.The samples from four typical Hungarian varieties were in climate box, and the thermal effects examined by infrared camera. In the laboratory curing box the limit values of tobacco curing were controlled (temperature, relative humidity), sothe thermal paramteres could be determined in depending on the usual characteristics (water-content of leaf, temperatura and humidity of curing air, variety, curing period).