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Abstract This study presents a data-driven spatial interpolation algorithm based on physics-informed graph neural networks used to develop a thermal Earth model for the conterminous United States. The model was trained to approximately satisfy Fourier’s Law of conductive heat transfer by simultaneously predicting subsurface temperature, surface heat flow, and rock thermal conductivity. In addition to bottomhole temperature measurements, we incorporated other spatial and physical quantities as model inputs, such as depth, geographic coordinates, elevation, sediment thickness, magnetic anomaly, gravity anomaly, gamma-ray flux of radioactive elements, seismicity, electrical conductivity, and proximity to faults and volcanoes. With a spatial resolution of $$18 \ km^2$$ 18 k m 2 per grid cell, we predicted heat flow at surface as well as temperature and rock thermal conductivity across depths of $$0-7 \ km$$ 0 - 7 k m at an interval of $$1 \ km$$ 1 k m . Our model showed temperature, surface heat flow and thermal conductivity mean absolute errors of $$6.4^\circ C$$ 6 . 4 ∘ C , $$6.9 \ mW/m^2$$ 6.9 m W / m 2 and $$0.04 \ W/m-K$$ 0.04 W / m - K , respectively. This thorough modeling of the Earth’s thermal processes is crucial to understanding subsurface phenomena and exploiting natural underground resources. Our thermal Earth model is available as web application at https://stm.stanford.edu , feature layers on ArcGIS at https://arcg.is/nLzzT0 , and tabulated data on the Geothermal Data Repository at https://gdr.openei.org/submissions/1592 .

Heat flow data obtained in connection with geothermal resource exploration suggests anomalous upper crustal structure and processes in parts of central east Tasmania. The regional scale crustal geology of the Midlands of Tasmania is, however, mostly obscured at the surface by the Permo-Triassic sedimentary sequences of the Tasmania Basin together with extensive exposures of Jurassic dolerite. We investigate controls on undercover crustal processes in this region by combining long period and broadband magnetotelluric (MT) datasets in 3D inversions for the geoelectric structure; followed by an interpretation that is informed by aspects of the pre-existing 3D regional geological and geophysical model. The new 3D model allows improved resolution of low resistivity anomalies together with a qualitative appraisal of spatially variable model sensitivity. The most robust features ( $ \lt 1\,\Omega {\rm m} $ < 1 Ω m ) in the 2–3 km depth interval occur where N–S and E–W faults intersect with a high point in the topography of the upper surface of a deep seated granite body. Enhancement of conductivity in this zone by clay, graphite or mineralisation, or a combination thereof, is likely. Other low resistivity features suggest that conductive pathways exist where major or multiple faults are present. These interpretations provide support for continued exploration in the Midlands of Tasmania for a variety of resources related to crustal fluids and fracturing. [ABSTRACT FROM AUTHOR]

SUMMARY: Greenland's tectonic history is complex, and the resulting lithospheric structure is, although extensively researched, not well constrained. In this study, we model the lithospheric structure of Greenland in a consistent, integrated framework with three steps. First, we build a lithospheric background model by forward modelling, adjusted to gravity gradient data and shear wave velocities from a regional tomography model. Subsequently, we jointly invert for the upper crustal density and susceptibility structure by minimizing the gravity residuals and magnetic total field anomaly misfit. The last modelling step searches for upper crustal thermal parameters to fit our model to the most recent geothermal heat flow predictions for Greenland. Finally, we present 3-D models of the density, temperature and velocity structure for the lithosphere as well as thermal parameters and susceptibilities for the upper crust. Our model also includes the depth of the Moho and LAB in Greenland. A comparison between inverted crustal parameters and surface geology shows a clear correlation. The novelty of our model is that all these results are consistent with each other and simultaneously explain a wide range of observed data. [ABSTRACT FROM AUTHOR]

Abstract The Ethiopia Rift System (ERS) is a section of the East African Rift System within Ethiopia extending from the Afar in the northeast to the Kenya border in the southwest. It is apparent that magmatism and magmatic intrusions influence the crustal shape in the ERS resulting in its thinning and the shallowing of magmatic sources at various locations within it. As a consequence, more than 31 volcanoes hosting hydrothermal structures with a conceivable potential to generate massive quantities of geothermal energy have been identified along the ERS. In this study, we map the Curie Point Depth (CDP) over the ERS based on the analysis of aeromagnetic data extracted from the World Digital Magnetic Anomaly Map. Spectral evaluation method was used to estimate the boundaries (top and bottom) of the magnetized crust. Reduced-to-pole (RTP) aeromagnetic records have been divided into 105 (50% overlap) square blocks of 200 × 200 km size. The Curie temperature (580 °C) of magnetite was used to determine the thermal gradient and the heat drift in the area. The depths obtained for the bottom of the magnetized crust are assumed to correspond to the Curie Depths, where the magnetic layer loses all its magnetization. The determined values of Curie Point Depth, geothermal gradient and heat flow for the 50% overlapped 105 blocks, respectively, range from 8.85 to 55.85 km, 10.38 to 65.54 °C/km and 25.96 to 163.84 mW/m2. Lower CPD (

Ground temperature survey at three thermal fields of the southern group of the Kambalny volcanic ridge (South Kambalny Near, Central and Far thermal fields) was carried out. Their current state is characterized. The formation of temperature anomalies is determined by the peculiarities of the geological structure of each thermal field.The maps of temperature surveys obtained in 2021 and 1965 are compared. Changes in the conditions of convective heat flow unloading in the geologic structure of thermal fields are shown. The size of temperature fields on all geologic structures of the southern group of the Kambalny volcanic ridge have significantly increased over time. The area of the most warmed areas of thermoanomalies has increased. The maximum ground temperatures increased by 10 °С on average. Some thermoanomalies (boiling and pulsating water boilers and vapor-gas jets) increased their flow rates and (or) temperature. New warmed areas within the thermal anomalies were discovered.

Objective The geothermal field in the present sedimentary basin is a result of the energy balance between various dynamic processes on the Earth. It serves as an important tool for understanding continental dynamics, such as tectonic deformation and the evolution of the continental lithosphere. Additionally, it provides the basis for evaluating regional geothermal resources. Methods A comprehensive study of the geothermal field in the entire Songliao Basin was conducted using oil-test temperatures from 826 wells and thermal conductivities measured by the optical scanning method. Formation temperatures at depths of 1 000 m, 2 000 m, 3 000 m, and 4 000 m were estimated using deep temperature prediction technology. Results The results indicate that the present geothermal gradient in the Songliao Basin ranges from 22.5 to 69.0℃/km, with an average of 44.0℃/km. The thermal conductivity values of rocks in the central depression area are relatively concentrated, mostly ranging from 1.60 W/(m·K) to 2.40 W/(m·K), with an average of 1.84 W/(m·K). Among these, mudstone has the lowest thermal conductivity, with an average of 1.77 W/(m·K); siltstone has a middle range with an average of 1.87 W/(m·K); and fine sandstone has the highest thermal conductivity, with an average of 2.12 W/(m·K). The heat flow ranges from 35.0 to 98.8 mW/m2, with an average of 76.9 mW/m2. The basin exhibits a typical "hot basin" characteristic, with higher heat flow in the central depression and lower heat flow in the slope and uplift areas, forming an annular distribution pattern. Geothermal anomaly areas are distributed in the northeast of the central depression and the northwest of the southeastern uplifted region. The formation temperature at a depth of 1, 000 m ranges from 26.9 to 72.3℃, with an average of 47.9℃; at 2 000 m, it ranges from 49.4 to 141.3℃, with an average of 91.9℃; at 3 000 m, it ranges from 71.8 to 167.5℃, with an average of 135.8℃; and at 4 000 m, it ranges from 94.3 to 210.9℃, with an average of 179.8℃. Conclusion These findings suggest that the subduction of the Pacific Plate beneath the Eurasian Plate has caused upwelling of the asthenosphere and rapid thinning of the regional lithosphere, resulting in a significant increase in heat from the mantle. Simultaneously, the thinned crust facilitates the upward conduction of mantle heat. The widespread NNE and NW fault systems in the basin provide channels for the rise of mantle material and heat flow. Some mantle material remains in the middle and lower crust along deep faults, forming high-conductivity and low-velocity bodies that continuously heat the crust. A portion of the volcanic activity in the Songliao Basin is attributed to the eruption of Cenozoic volcanoes through faults. The presence of granite in the basin's basement plays a significant role in generating heat through the decay of radioactive elements, thereby serving as an important heat source. The heterogeneity of the current geothermal field can be attributed to variations in crustal structure among different tectonic units. The difference in thermal conductivity between the basement and sedimentary layers leads to a "refraction" effect on heat flow, resulting in the redistribution of heat in the shallow part of the basin and the formation of a distinct heat flow distribution pattern between concave and convex areas. The favorable combination of reservoir capacity in the Songliao Basin provides ideal conditions for heat storage, making it conducive for the development of low- and medium-temperature geothermal resources.

Abstract Estimates of heat flow can contribute to our understanding of geological structures in plate convergent zones that produce great earthquakes. We applied automated velocity analysis to obtain the accurate seismic profiles needed for precise heat flow estimates using six new seismic profiles acquired during R/V Kaimei KM18-10 voyage in 2018. We calculated heat flow values in the accretionary wedge of the Nankai Trough off the Kii Peninsula, Japan, from the positions of widespread bottom-simulating reflectors (BSRs) in seismic reflection profiles. Calculated conductive heat flow values from the depth of the BSR agree with previous studies where a regional trend is observed from ~ 50 mW/m2 to

The thermo-rheological structure of the lithosphere is an effective method to reveal the thermal state within the lithosphere. Studies of the thermo-rheological structure of the lithosphere in geothermal anomaly areas can effectively constrain the contribution of heat sources. The southeastern China is an important distribution region for geothermal resources, with a large number of natural hot springs emerging on the land surface. Boreholes in this region have identified high geothermal gradients at depth. However, the mechanism of the heat sources is still controversial, and whether the hot dry rock resources exists is not clear. In this study, we take the Huangshadong geothermal field in Huizhou of Guangdong as the research target. We analyze the temperature distribution and rheological strength of the lithosphere, discuss the heat sources of the Huangshadong geothermal field, examine the thermal influence of shallow hydrothermal systems, and predict the prospects of dry hot rock resources. The results show that the heat flux under the influence of hydrothermal systems in the Huangshadong geothermal field is 130.3 mW/m2, and the crustal heat flow is similar to the mantle heat flow, showing a warm-crust-warm-mantle lithospheric thermal structure. In addition, the structural heat flux reaches 30.5–60.3 mW/m2. The rheological structure of the lithosphere shows that the middle crust has a ductile rheological layer, the upper crust and the lower crust are mainly controlled by brittle failure, and the lower crust and the lithosphere mantle show coupling in the rheological structure, which indicates a relatively stable crustal bottom boundary. The heat sources of the Huangshadong geothermal field is dominated by the tectonic heat source, and the mantle heat source and radiogenic heat production are the main heat source components. The main parts of tectonic heat source include the heat accumulation in regional deep faults and cyclic heat transfer in hydrothermal systems, both of which may carry heat to the surface through “relay” heat transfer. The proportion of heat accumulation of regional deep faults in the tectonic heat source is the key factor affecting the prospects of dry hot rock resources.

The geothermal field of the platform cover within the Grodno region is considered. The cover rests on a crystalline basement of Precambrian rocks. Temperature distribution maps for depths of 100; 200 and 300 m below ground level were compiled based on thermograms recorded in boreholes and were supplemented by the heat flow map. These reveal geothermal anomalies both of temperature and heat flow density distribution within the region. The temperature in the region monotonously increases with depth, while preserving the general features of the thermal field. The anomalies identified on the 100 m map persist for depths of 200 and 300 m. The main role in the formation of temperature anomalies is played by near-surface factors, such as groundwater circulation, and the influence of paleoclimatic changes on the Earth’s surface in the past. A low heat flow (< 30 mW/m2) in the eastern part of the region gradually increases up to 50 mW/m2 in the vicinity of Grodno. Its areal variation relates to the distribution of granitoid and blastomylonite rocks in the crystalline basement. Increased heat flow is typical of silicic rock massifs with elevated concentrations of long-living radioactive isotopes of uranium, thorium and potassium. Their decay creates an additional radiogenic component of heat flow.

The potential of high-temperature $({>}150~\text{°}\mathrm{C})$ geothermal systems in crustal fault zones (fault cores and hundreds of meters wide networks of interconnected fractures in the damage zone) is underestimated. Based on numerical models, we show that topography-driven, poroelasticity-driven as well as buoyancy-driven forces play a significant role in the establishment of shallow (1–4 km) thermal anomalies in fault zones. We investigate the role of permeability, topography, fault dip, tectonic regime and fault geometry on the amplitude of thermal anomalies. Favorable conditions include: (i) a damage zone thickness $>$ 100 m, (ii) a minimum cumulative displacement of 100–150 m and (iii) fault zone lengths of at least one kilometer. Based on these parameters, we propose new potential targets for the geothermal exploration of fault zones in Western Europe.

Abstract The Thrace Basin in northwestern Turkey is a deep Eocene–Oligocene hydrocarbon-bearing sedimentary basin. The basin has potential for geothermal energy utilization in the future due to its favorable geological conditions. In this study, we combined the available bottom hole temperature (BHT) data from 70 points with the thermal conductivity and radiogenic heat productions of the basin formations, and generated a detailed thermal model of the northern part of the basin. For heat flow determinations from the BHT data, we applied Bullard’s thermal resistance method on formation thermal conductivities and thicknesses. The results give an average surface heat flow of 65.8 ± 11.3 mW/m2. We obtained high heat flow values (75–80 mW/m2) in the eastern and western sides, and the central part of the study area. These relatively high heat flow values can be explained by the combined effect of basement topography and the variations in the radiogenic heat production of the basement rocks. The calculated subsurface temperatures in selected hydrocarbon fields vary in the range of 45–64 °C at 1 km depth, 99–136 °C at 3 km depth, and 155–208 °C at 5 km depth as a result of local variations of the surface heat flow and formation thermal resistances. These variations in subsurface temperatures can have significant effects on the cost of geothermal energy production in future.

Heat flow in the Northern Mozambique Channel is poorly constrained, with only a few old measurements indicating relatively low values of 55–$62~\text{mW/m}^2$. During the SISMAORE cruise to the Northern Mozambique Channel, we obtained new heat flow measurements at four sites, using sediment corers equipped with thermal probes. Three of the sites yield values of 42–47 $\text{mW/m}^2$, confirming low regional heat flow in this area. Our values are consistent with a Jurassic oceanic lithosphere around Mayotte, although the presence of very thin continental crust or continental fragments could also explain the observed heat flow. Our values do not support a regional thermal anomaly and so do not favor a hotspot model for Mayotte. However, at a fourth site located 30 km east of the submarine volcano that appeared in 2018 east of Mayotte, we measured a very high heat flow value of $235~\text{mW/m}^2$, which we relate to the circulation of hot fluids linked to recent magmatic activity.

Abstract New heat flow data corrected for climate change over Northeastern Japan were obtained using the temperature profile of the borehole of the High Sensitivity Seismograph Network (Hi-net). The obtained spatial distribution of heat flow shows low heat flow on the forearc side, high heat flow along the Ou Backbone Range, and low heat flow in the plains on the back-arc side. However, the distribution is not clearly divided into high and low heat flow along the VF front; for example, the low heat flow extends from near the northern Kitakami Mountains on the forearc side to the Ou Backbone Range crossing the VF, while the high heat flow extends to the central Kitakami Mountains and Sendai plain on the forearc side. In addition, a crustal temperature structure model was developed that considers into account the presence of sedimentary layers, the temperature dependence of thermal conductivity, and differences in heat generation due to lithology. There is a good correlation between this temperature structure and the lower limit of the seismogenic layer, which is between 400 and 450 °C. Compared to previous studies, the crustal thermal structure calculation method assumed is a model whose estimated temperature distribution is sensitive to structural differences; however, a more accurate estimation of the temperature structure is possible if detailed structural information is available. On the other hand, it seems necessary to treat fluid behavior in more detail in areas of high heat flow. However, the estimation of crustal temperature structure, especially in regions with thick sedimentary layers, is considered an improvement over the previous study. Graphical Abstract

Abstract Aristino-Traianoupolis area hosts one of the most significant water-dominated low-temperature geothermal fields in Greece. It is located on the southwestern uplifted margin of the Tertiary Evros Delta molassic basin, 10 km east of the town of Alexandroupolis (Thrace, NE Greece). The upper hydrothermal system of the Aristino Geothermal Field (AGF), one of the most promising in continental Greece, contains fluids with temperatures ranging from 51 to 99 °C, within a series of overlapping aquifers at very low depths (100–430 m). The main geothermal anomaly for temperatures higher than 90 °C covers an area of 6 km2, to a maximum prospected depth of 500 m below ground surface. The scattered regional anomaly exceeds 50 km2 and is characterized by excessively high and abruptly changing thermal gradient (42 to 450 °C/km) and heat flow (80–800 mW/m2), that are both typical of a fault-controlled hydrothermal system. Since 1993, the AGF has undergone non-systematic geothermal investigation, with emphasis on low-depth (100–500 m) drilling. This paper provides, for the first time, a synthetic and detailed evaluation of all available temperature data gathered in the last 25 years. The steady-state temperature logs reveal the dominant role of conduction for the upper geothermal system, accompanied, in most cases, by rapidly changing and abnormally high thermal gradients (100–450 °C/km), triggered, most probably, by a deeper system of higher temperature. This hypothesis is also supported by the applied chemical geothermometers, which suggest initial fluid temperatures at 140–150 °C, the hydrochemical characteristics of the fluids hosted in the deeper and most promising investigated reservoir (ignimbrite) of the upper system, and the extrapolated temperatures from the conductive temperature–depth profiles. The lower widespread medium enthalpy hydrothermal system should extend at depths 500–1000 m within volcanics and the expected Eocene limestones and basal clastic series of the Tertiary sequence that have filled the basin. Nevertheless, these assumptions need to be verified by appropriate investigations and new drillings at depths greater than 600–700 m, which would confirm the presence of a productive medium enthalpy reservoir.

Abstract Heat flow across oceanic transform faults (TFs) and fracture zones (FZs) has rarely been studied in detail, despite these features representing distinct thermal boundaries within the oceanic lithosphere. Here, we present heat flow measurements across the St Paul fracture zone (SPFZ) in the equatorial Atlantic Ocean, from 48 Ma crust in the south to 71 Ma in the north. To the north of the FZ we find a basal heat flow of 63 mWm−2, and to the south a basal heat flow of 79 mWm−2, both in agreement with plate cooling models. However, within the SPFZ we find a heat flow of 83 mWm−2, greater than the values of the adjacent crust and 10–15 mWm−2 higher than predicted from conductive cooling models, suggesting that the thermal structure of the FZ has been modified. Evidence from seismic and sub‐bottom profiler data indicate recent active deformation within the SPFZ, potentially driven by lithospheric flexure across the FZ or temporal changes in TF configuration. We propose that this deformation may enable fluid circulation and heat advection within the basement, creating the seafloor heat flow anomaly within the FZ. These findings suggest that FZs may remain important zones predisposed to host deformation and fluid flow in the oceanic lithosphere, despite not being active plate boundaries.

The estimation of the Curie point depth (CPD) and heat flow (HF) from magnetic data is useful for geothermal and tectonic studies. However, the methodology of estimating these values is still controversial as numerous studies have used different types of transformed magnetic data. Most studies utilize the total magnetic intensity (TMI) or the reduced to the pole (RTP) data, and since shallow magnetic bodies may affect the final CPD values, low-pass (LP) wavelength filtering has also been used to estimate the CPD. In this study, the two-dimensional radially averaged spectral analysis was applied to the land-based magnetic data from the Sinai Peninsula. TMI and RTP data were both analyzed, using different LP filtered wavelengths, and the final CPD and HF values were compared. The cut-off wavelength parameter was selected in terms of the geologic complexity. The results show that the estimated CPD values are well correlated regardless of whether the magnetic data were either TMI or RTP. The RTP data produced a spatial shift in the CPD smaller than the window size being used. Additionally, the centroid method is primarily dependent on the wavenumber, which varied slightly on applying the RTP. There were slight differences in the estimated CPDs when a short LP filter (e.g., 20 km) was applied, whereas increasing the wavelength (e.g., 40 km) caused the CPD values to increase exceeding the plausible depth limits, and the associated spatial trends varied when compared to the other methods. In areas where the basement rocks were shallow or exposed, a LP filter can be applied with short cut-off wavelength. The estimated CPDs were discussed in the context of seismicity data, gravity-based Moho depths, and HF measurements.

ABSTRACT: Great advancement has been made on natural gas hydrates exploration and test production in the northern South China Sea. However, there remains a lot of key questions yet to be resolved, particularly about the mechanisms and the controls of gas hydrates enrichment. Numerical simulaution would play signficant role in addressing these questions. This study focused on the gas hydrate exploration in the Shenhu Area, Northern South China Sea. Based on the newly obtained borehole and multichannel reflection seismic data, the authors conducted an integrated 3D basin modeling study on gas hydrate. The results indicate that the Shenhu Area has favorable conditions for gas hydrate accumulation, such as temperature, pressure, hydrocarbon source, and tectonic setting. Gas hydrates are most concentrated in the Late Miocene strata, particularly in the structual highs between the Baiyun Sag and the Liwan Sag, and area to the south of it. It also proved the existence of overpressure in the main sag of source rocks, which was subject to compaction disequilibrium and hydrocarbon generation. It also shown that the regional fault activity is not conducive to gas hydrate accumulation due to excess gas seepage. The authors conjecture that fault activity may slightly weaken overpressure for the positive effect of hydrocarbon expulsion and areas lacking regional fault activity have better potential.©2022 China Geology Editorial Office.

Geochemical and lithological investigations in the WON C-3X well record five organic-matter-rich intervals (OMRIs) of effective source rocks. These OMRIs correspond to moderate and good potentials. Two of these intervals occurred within the L-Kharita member of the Albian age represent 60.97% of the entire Albian thickness. The rest of OMRIs belongs to the Abu-Roash G and F members of the Late Cenomanian–Santonian age comprising 17.52 and 78.66% of their total thickness, respectively. The calculated heat flow of the studied basin is high within the range of 90.1–95.55 mW/m2 from shallower Abu-Roash F to deeper L-Kharita members. This high-heat flow is efficient for shallowing in the maximum threshold expulsion depth in the studied well to 2,000 m and active source rock depth limit to 2,750 m. Thermal maturity and burial history show that the source rock of L-Kharita entered the oil generation from 97 Ma till the late oil stage of 7.5 Ma, whereas the younger Abu-Roash G and F members have entered oil generation since 56 Ma and not reached peak oil yet. Hence, the source rock intervals from Abu-Roash F and G are promising for adequate oil generation.

Abstract A three‐dimensional (3D) finite element model was built to understand the lunar surface and subsurface thermophysical behavior. This is a multi‐layer model, with a top porous layer followed by denser layer(s) beneath, with several advantages. The model can incorporate complex geometry, different sizes and parametric‐based variation in physical properties for individual layers and can be implemented at various scales. At present, the model can account for local to regional scale variations and can be improved further to predict global scale variations. The diurnal evolution of surface and subsurface temperatures from the model showed a clear effect of the outermost porous layer on the heat propagation into the subsurface as predicted from earlier studies. Being a 3D model, it is capable of simulating significant variations in lateral heat transport due to presence of topography to derive realistic surface and near‐surface temperatures on the Moon. The model results were validated through laboratory experiments, Apollo in situ data and compared with those from earlier models. The unique feature of the model is that it allows to use any Digital Elevation Model (DEM) for any site of interest which is demonstrated in this work by considering a case study of the Apollo‐17 landing site to derive its thermophysical behavior. In addition to being an important tool for addressing several geophysical problems, the model can largely aid in planning and execution of future in situ exploration of the Moon. This model is a first step toward building a comprehensive large‐scale model for understanding the thermophysical behavior of the Moon.

Abstract High‐quality maps of Geothermal heat flow (GHF) are crucial when modeling ice dynamics, shape, and mass loss of the Antarctic Ice Sheet, which is one of the largest potential contributors to sea level rise. The determination of GHF remains challenging, as in situ data are sparse and geophysical models exhibit large discrepancies in amplitude and resolution, especially on regional scales. Using a novel approach implementing a joint inversion of gravity and seismic tomography data with various geophysical and mineral physics information, we estimate the 3D thermal lithospheric structure and present a new GHF map. The resulting surface heat flow correlates with the location of subglacial volcanism and can represent a boundary condition for accurate ice dynamics models that can explain observed acceleration in the ongoing ice mass loss. Absolute values are within the range of other seismology‐based methods and are much lower than those obtained using for example, magnetic data. High uncertainties remain in the parametrization of the upper crustal structure and thermal parameters.

This study aims to analyze the complex relationship between heat flow and seismicity in tectonically active zones worldwide. The problem was quantitatively analyzed by using a geographic detector method, which is well suited for analyzing nonlinear relationships in geography. Moreover, β-value that describes the frequency-magnitude distribution is used to represent the seismicity. The results showed that heat flow (HF) = 84 mW/m2 is a critical point for the relevant mechanisms of heat flow with seismicity in these zones. When HF < 84 mW/m2, the heat flow correlates negatively with the β-value, with a correlation degree of 0.394. Within this interval, buoyant is a primary control on the stress state and earthquake size distribution. Large earthquakes occur more frequently in subduction zones with younger slabs that are more buoyant. Due to zones with a high ratio of large earthquake corresponds to low β-values, high heat flow values correspond to low β-values. When HF > 84 mW/m2, the heat flow correlates positively with the β-value, with a correlation degree of 0.463. Within this interval, the increased heat flow decreases the viscosity of the rock plate and then reduces the stress. Lower stress would correspond to a smaller earthquake and then a higher β-value. Therefore, high heat flow values correspond to high β-values. This research would be conducive to understand the geologic activity and be helpful to determine the accuracy and timeliness of seismic hazard assessment.

Geophysical study involving aeromagnetic method was carried out to investigate parts of Niger Delta in Nigeria, aimed at investigating the cause and nature of anomalous bodies within the study area. Spectral analysis technique was employed in quantitative interpretation to determine depth/thickness of the sedimentary basin, basement topography, structural trends, curie point depth, thermal gradient and heat flow in the area. The total magnetic intensity (TMI) anomalies had values of between -53.7nT and 119.5nT while the residual magnetic intensity ranged from -52.5 to 58.0nT. The spectral analysis revealed the depth to magnetic sources varying from 2.5 to 5.5km while the shallow magnetic sources varied from 0.89 to 1.47km. The geothermal analysis revealed the curie point depth between 11.782 and 18.048km while the calculated geothermal gradient ranged lie between 32.137 and 49.231o𝐶𝑘𝑚−1. The heat flow values ranged from 80.343 to 123.080𝑚𝑊𝑚−2. The results from this study have thrown more light to the understanding of the variation of subsurface structures in the study area. These will enhance the development of the resources and will be of economic benefit to the country if well harnessed. However, possible future research work on this active area is proposed for more robust results.

The first determinations of the heat flow density in Uzbekistan, as well as in Central Asia as a whole, were carried out in the middle 1960s. In subsequent years, many researchers, primarily in connection with the search and exploration of oil and natural gas deposits, studied the geothermal field of the region. The data accumulated to date show a significant heterogeneity of the thermal field in both Uzbekistan and the adjacent territory of Central Asia. Rare wells were studied in the desert areas of Kyzyl Kum and Kara Kum. The heat flow in Uzbekistan varies over a wide range from 20–30 to approximately 100 mW/m2. Its high values are characteristic of intermountain depressions and blocks of the earth’s crust with a dense network of deep faults. The heat flow increases significantly in the southern and eastern parts of Uzbekistan, as well as in the neighbouring territories adjacent to the mountain structures of the Tien Shan and Pamir, characterized by high seismicity, tectonic and thermal activation. An updated map of the heat flow density of Uzbekistan was compiled and, separately for the Fergana Depression. They reflect a significant regional variability of the geothermal field. With the transition from the relatively flat territory of the Turanian Plate to mountain structures, the degree of differentiation by the heat flow increases significantly. This is typical of the entire orogenic Alpine-Himalayan Belt.

The heat-flow history of the Putumayo Sub-Basin has undergone a long-term and complex evolutionary process from the Late Mesozoic to the Cenozoic due to multiphases of tectonic evolution. The regional geologic background and the forward modeling of paleo-temperature were applied to determine the heat-flow value during different stages ever since the Cretaceous. The heat-flow value was 64 mW/m2 in the Cretaceous, 95 mW/m2 in the Paleocene, 38 mW/m2 at the end of Oligocene, 120 to 190 mW/m2 (increasing from east to west and averaging 155 mW/m2) in the Pliocene, and 55 mW/m2 at present.

In the South of Kamchatka, modern geodynamic processes are actively taking place. A deep geological and geophysical model of the structure of the earth’s crust and upper mantle along the regional profile of the Apacha Village -Mutnaya Bay in the zone of Tolmachevsky active magmatic center (TAMC) is presented. The profile passes near the South-Western border of the Karymshinskaya volcano-tectonic structure (VTS) and crosses the Ahomtenskaya VTS. The model created on the basis of integrated interpretation of materials of the earthquake converted-wave method (ECWM), gravity and magnetotelluric sounding (MTS). The thickness of the earth’s crust along the profile varies from 30-33 km at the edges reaching 44-46 km, in its Central part. The dominant feature of the model is a high-density formation – a block of the earth’s crust, saturated with intrusions of the main and ultrabasic composition. The formation of the block is associated with a permeable zone between the crust and the upper mantle. In the block correlation of seismic boundaries is disturbed and in a density model the area with massive heterogeneity is allocated. A significant increase in depth to the M-Boundary in the center of the model is explained by the presence of a “bloated” transition layer between bark and mantle in this place. The thickness of the layer is about 10 km, and the density of the mantle reaches 3,4 g/cm3. It is supposed that it is a site of eklogization of breeds in a zone of paleosubduction of oceanic lithosphere under a continental. The area is favorable for the accumulation of meteor waters, which are in contact with high-temperature environment and postmagmatic solutions of intrusions, which leads to the formation of hydrothermal systems. The genetic connection of Karymshinsky gold- ore cluster with the intrusive array of medium-sour composition, allocated in the zone of the Tolmachevsky active Magmatic Center is shown.

We present laboratory and numerical models investigating the behavioural regimes of rapidly rotating convection in high-latitude planetary core-style settings. Our combined laboratorynumerical approach, utilizing simplified geometries, can access more extreme parameters (e.g. Rayleigh numbers Ra ≲ 1013; Nusselt numbers Nu ≲ 103; Ekman numbers E ≳ 3 × 10-8) than current global-scale dynamo simulations. Using flow visualizations and heat transfer measurements, we study the axialized flows that exist near the onset of rotating convection, as well as the 3-D flows that develop with stronger forcing. With water as the working fluid (Prandtl number Pr ≲ 7), we find a steep scaling trend for rapidly rotating convective heat transfer, Nu~(Ra/RaC)3.6, that is associated with the existence of coherent, axialized columns. This rapidly rotating trend is steeper than the trends found at moderate values of the Ekman number, and continues a trend of ever-steepening scalings as the rotation rate of the system is increased. In contrast, in more strongly forced or lower rotation rate cases, the heat transfer scaling consistently follows a shallower slope equivalent to that of non-rotating convection systems. The steep heat transfer scaling in the columnar convection regime, corroborated by our laboratory flow visualizations, imply that coherent, axial columns have a relatively narrow range of stability. Thus, we hypothesize that coherent convection columns are not stable in planetary core settings,where the Ekman number is estimated to be~10-15. As a consequence, convective motions in the core may not be related to the columnar motions found in presentday global-scale models. Instead, we hypothesize that turbulent rotating convection cascades energy upwards from 3-D motions to large-scale quasi-2-D flow structures that are capable of efficiently generating planetary-scale magnetic fields. We argue that the turbulent regimes of rapidly rotating convection are essential aspects of core dynamics and will be necessary components of robust, next-generation and multiscale dynamo models.

Abstract The strength of faults was vigorously debated for years, but lately a growing number of studies suggest that faults are weaker than originally suggested. Nonetheless, only a handful of natural faults have been studied in detail, and only one, the San Andreas, is a strike‐slip fault. Here, we reanalyze 268 surface heat flow measurements taken in the proximity of the southern Dead Sea Transform fault to evaluate its friction. To account for large terrain relief, and the presence of salt diapirs, we apply 3‐D terrain and salt diapir corrections. Based on these corrected heat flow values we estimate that the long‐term frictional resistance of the Dead Sea fault is 0.28 ± 0.17. This low value is similar to friction estimates from the San Andreas fault and several subduction zones.

Abstract Fifty new heat flow measurements from the Chukchi Borderland (CBL) and adjacent regions of the central Arctic Ocean are reported, where heat flow measurements have been very limited. The average heat flow of the CBL (65 mW/m2) is significantly higher than that of the entire Amerasia Basin (53 mW/m2). In the CBL, the heat flow of the Chukchi Plateau (CP), Northwind Basin (NWB), and Northwind Ridge (NWR) are 64 mW/m2, 69 mW/m2, and 60 mW/m2, respectively. With the aid of nearby seismic profiles, the elevated regional heat flow in the CP and NWR was attributed to the enhanced radiogenic heating of the thick crust (25–29 km), while the most prominent heat flow in the relatively thin crust of the NWB is likely due to the residual heat of a major tectonic extension event. Further numerical heat conduction modeling suggests that the initial rifting of the Amerasia Basin during the Jurassic–Early Cretaceous could not induce such high heat flow in the NWB. Together with recent interpretations of seismic profiles, the elevated heat flow in the NWB could be explained by the residual heat of the Late Cretaceous–early Cenozoic extension. This extension event was contemporaneous with the seafloor spreading in the Makarov Basin and had also been associated with the onset of seafloor spreading in the Eurasia Basin.

• Mimas could have grown an ocean as its eccentricity decreased to its present value. • The onset of melting had to occur when Mimas' eccentricity was 2–3 times the present value. • A thinning ice shell over the past ∼10 Myr of Mimas' evolution is consistent with its geology. The fractured, young surfaces on confirmed ocean worlds such as Europa and Enceladus suggest that ocean-bearing moons with relatively thin overlying ice shells should be easy to identify. Hence, the discovery that Mimas' rotation state is best explained by an internal ocean seems challenging to reconcile with its heavily cratered surface. Previous studies have shown that an internal ocean is compatible with Mimas' geology as long as the ice shell has been thinning throughout the surface age. This scenario has yet to be placed into context within Mimas' thermal-orbital history, in particular, the link between tidal dissipation and orbit circularization. Here, we model Mimas' coupled thermal-orbital evolution, and the implications of an emerging ocean on Mimas' geology, to determine whether a thinning ice shell is feasible. We find that the ice shell can thin – and the ocean grow – even as the eccentricity decays due to tidal dissipation as long as the ocean formed within the past 10 – 15 million years and the onset of melting occurred when Mimas' eccentricity was between 2.5 and 3 times the present-day value. As Mimas' eccentricity continues to decay, the ocean will likely enter an epoch of freezing, leading to fractures within the ice shell and eruptions of ocean material at the surface, before freezing completely. These results suggest that Mimas, Enceladus, and Tethys may represent three points along a continuum of ocean initiation, growth, and loss. [ABSTRACT FROM AUTHOR]

Abstract The (HP 3) of the InSight Mars mission is an instrument package to measure the Martian geothermal heat flow. The instrument's platinum resistance temperature sensors have been calibrated between −75 and +55 °C, and the absolute temperature uncertainty of the calibration is 10 mK. Temperature differences can be measured with an uncertainty of better than 5 mK. HP 3 determines regolith thermal conductivity by using the HP 3 mole as a modified line heat source, and thermal conductivity can be measured with an uncertainty of better than 4%. Tilt sensors used to determine the attitude of the mole during penetration measure tilt with an uncertainty of better than 0.25°.

Heat flow data from the Eastern Mediterranean region indicates an extensive province of low heat flow, spreading over the whole basin of the Mediterranean to the east of Crete (Levantine Sea), Cyprus, and Northern Egypt. Surface geology of East Anatolia is complex because of recent active tectonic and volcanic activity. The region is composed of major tectonic units of Pontides, the Anatolid-Tauride Belt and Bitlis Suture Zone, North and East Anatolian faults. Ophiolitic and young volcanic rocks can be observed in many parts of East Anatolia. The Black Sea is surrounded by the Alpine-Himalayan Orogenic Belt of Crimea, Greater Caucasus, Pontides, Rhodope-Stranja Massif, Eastern Srednegorie, North Dobrogea and older tectonic units of different origins and ages such as the Precambrian East European Craton, Moesian Platform, Istanbul Zone and Adzhar-Trialet Folded System. Low heat flow density dominates in the Black Sea. The lowest (less•30 mW/m2 ) values have been recorded in central parts of the Western and Eastern Black Sea basins with maximal sedimentary thickness. Geothermal studies within the territories of Ukraine have been under way since sixties. Many important features of the thermal field remain unstudied. This applies in particular to the Ukrainian Shield and to the southern part of the Carpathian region. In general, the territory of Alpine folding within Turkey, Marmara and Aegean seas, Caucasus is characterized by high heat flow. The anomaly of its highest values (above 100 –150 mW/m2 ) exists within western Turkey, where tectonic conditions of extension prevail and underground steam is used to produce electricity. Three heat flow density profiles crossing the studied region and heat flow map were compiled.

A traditional approach for heat flow determination requires two parameters. They are a geothermal gradient and heat conductivity of rocks comprising the considered depth interval. The geothermal gradient is determined from a thermogram recorded in a wellbore and the heat conductivity is obtained from the laboratory measurements of selected rock samp les. There are some variations of this approach to both get the gradient and heat conductivity values. However, there are many areas without boreholes to register their thermograms, or at least to have several temperature readings at intermediate positions of bottom holes and traditional methods of heat flow determinations cannot be used. Recently another method was proposed to estimate heat flow. It was derived from spectral analysis of magnetic field. During last years it was widely used in Nigeria for areas where deep boreholes are absent. It uses estimates of depths to the base and bottom of the causative body derived from analysis of the magnetic field maps. The base of the causative body corres ponds to the depth of the Curie surface at which rocks lose their magnetic properties. It is known that it happens at the temperature around 580 °C that slightly varies depending on the content of magnetite within the causative body. The temperature at the top of this body is estimated. The heat flow density can be calculated knowing the geothermal gradient within this depth interval and heat conductivity of rocks. A preliminary heat flow density map was compiled based on all accessible heat flow data. A comparison of heat flow data from several regions of the country, determined using both methods provides rather good agreement.

According to the complex geothermal investigation results (thermal conductivity, rocks thermal heterogeneity measurements as well geothermal gradient and heat flow calculation) on Yuzhny Island of Novaya Zemlya archipelago (Pavlovskoye lead-zinc field), the paleotemperature on the surface in the historical past are modeled. The results of the climatic history reconstruction in this region are discussed. An earlier heat flow estimate on on Yuzhny Island of Novaya Zemlya archipelago (46 mW/m2) could be underestimated if we assume the glacier absence during the “Pleistocene / Holocene warming”. In this case, the calculated heat flow will be 55 mW/m2. If during the “small glacial period” the glacier existence lasted for 20 thousand years, then the first heat flow estimate is more likely.

Abstract A geothermal exploration corehole was drilled to a total depth of 1821.5 m on the Mountain Home Air Force Base near Mountain Home, Idaho. The corehole was used to collect an unusually large amount of data, including uniaxial compressive stress (UCS) experiments on core samples, to evaluate the geothermal potential of the western Snake River Plain. In addition, unlike many exploration holes in this region, a fluid entry was encountered at 1745.3 m and flowed artesian to the surface. A maximum temperature of 149.4 °C was calculated for the entry. A temperature log run on the corehole from 3 to 1675 m is nearly linear with little variation. The average geothermal gradient is 73 °C/km, and the average heat flow between 200 and 1500 m is 102 ± 15 mW/m2. Chemical analyses of a sample from the fluid entry suggest that a significant proportion of the water is not meteoric. Five geothermometers show equilibrium temperature in the range of 133–157 °C. Furthermore, based on the unconfined UCS experiments on basalt core samples, a brittle unit was found to comprise the fractured reservoir that the geothermal water flows from, while an overlying ductile unit acts as a hydrothermal caprock. This implies that the reservoir/caprock pair may be a target for future exploration wells drilled to delineate the extent of the potential resource and the boundaries of the connected fracture network.

Abstract A Curie surface indicates the distribution of the thermal fields underground, providing a clear marker for the thermodynamic effect in the crust and mantle. In this paper, based on a geomagnetic field model (NGDC-720) and aeromagnetic data, we use power spectrum analysis of magnetic anomalies to estimate the Curie surface in Yunnan Province, China, and its adjacent areas. By combining the distribution of the Curie surface with regional heat flow, the geothermal gradient, crustal wave velocity ratio anomalies, high-conductivity layer anomalies, and the Moho surface, we reveal the connection between the undulation of the magnetic basement and the crustal structures. The results indicate that the uplift and depression of the Curie surface in the research area are distinct. The Curie surface is approximately inversely correlated to the surface heat flow. The Lijiang-Jianchuan-Baoshan-Tengchong and Jianchuan- Chuxiong- Kunming-Yuxi zones are two Curie surface uplift zones, and their crust-mantle heat flows are relatively high. The Curie surface uplift zone along the Lijiang-Xiaojinhe fault and Red River fault is consistent with the heading direction of the fault zone and is partially in agreement with the eastward mass flow of the Tibetan Plateau. The Curie surface uplift zone is consistent with the high wave velocity ratio and high-conductivity layer anomaly region of the crust. The depth of the Curie surface is less than the depth of the Moho surface.

Abstract Geothermal gradients were estimated at the points of a grid with cell size of 50 km by 50 km in northwestern Colombia. Depths to the bottom of magnetic sources were assumed to represent Curie depths, and were estimated by means of statistical-spectral analysis of aeromagnetic data contained in square windows of 100 km by 100 km, 200 km by 200 km, and 300 km by 300 km. The centroid method and a variation of it that considers the fractal distribution of magnetization were applied. The modified centroid method provided better estimations of Curie depths, which range between 13 km and 47 km. Obtained Curie depths are comparable to those reported in other studies of regional character. The corresponding estimated geothermal gradients correlate quite well with estimations based on the bottom simulating reflector and bottom hole temperatures. Observed differences are small and can be accounted for by local heat flow variations due to shallow ground water flow, or recent sedimentation. Elaborated geothermal gradient and heat flow maps for northwestern Colombia are accurate and consistent with estimates of the thickness of the oceanic crust and continental cortical thicknesses, reported by previous authors. The maps presented in this study represent a contribution to the heat flow studies in northwestern South America.

This study attempt to estimate the Curie point depth (CPD) and heat flow using high resolution aeromagnetic data over part of Bida basin bounded with longitude 5o00’E – 6o30’E and Latitude 8o30’N – 9o30’N with an estimated total area of 18,150 km2. We subjected the total magnetic intensity field of the study area to regional/residual separation using polynomial fitting. We divided the residual map into sixteen overlapping spectral blocks. We obtained centroid depths (Zo) and depth to top of basement (Zt)got from the plot of log of power spectrum against wave number; the centroid depth ranges from 6.61 km to 20.30 km while the depth to top of basement ranges from 1.59 km to 6.38 km. input parameter to calculate the curie depth (Zo). The CPD range from 10.88 km to 35.51 km with an average value of 23.22km. The CPD is deeper at the centre of the southern and eastern part of the study area which correspond to part of Pategi and part of Baro; and shallow at the northeastern and Northwestern part of the study area correspond to part of Mokwa and part of Bida. The geothermal gradients for the sixteen blocks range from 16.33 oCkm-1 at the centre of the southern region of the area to 53.30 oCkm-1 at the northeastern and north western region of the study area with an average of 28.98 oCkm-1. While the heat flow to range from 40.99 mWm-1 to 133.80 mWm-1 with an average value of 76.19 mWm-2. It can therefore be deduced from this study that the Southeastern, southwestern, and the northwestern part of the study area might be a good indicator of geothermal energy potential with minimum CPD, maximum geothermal gradient and heat flow since demagnetized rocks confirm a hot rock quantity in the crust that can be harnessed for geothermal energy exploitation.

Abstract A key feature of subduction zone geodynamics and thermal structure is the point at which the slab and mantle mechanically couple. This point defines the depth at which traction between slab and mantle begins to drive mantle wedge circulation and also corresponds with a rapid increase in temperature along the slab‐mantle interface. Here, we consider the effects of the backarc thermal structure and slab thermal parameter on coupling depth using two‐dimensional thermomechanical models of oceanic‐continental convergent margins. Coupling depth is strongly correlated with backarc lithospheric thickness, and weakly correlated with slab thermal parameter. Slab‐mantle coupling becomes significant where weak, hydrous antigorite reacts to form strong, anhydrous olivine and pyroxene along the slab‐mantle interface. Highly efficient (predominantly advective) heat transfer in the asthenospheric mantle wedge and inefficient (predominantly conductive) heat transfer in the lithospheric mantle wedge results in competing feedbacks that stabilize the antigorite‐out reaction at depths determined primarily by the mechanical thickness of the backarc lithosphere. For subduction zone segments where backarc lithospheric thickness can be inverted from surface heat flow, our results provide a regression model that can be applied with slab thermal parameter to predict coupling depth. Consistently high backarc heat flow in circum‐Pacific subduction zones suggests uniformly thin overriding plates likely regulated by lithospheric erosion caused by hydration and melting processes under volcanic arcs. This may also explain a common depth of slab‐mantle coupling globally.

Abstract While present heat flow (HF) throughout Israel and the Dead Sea Transform (DST) area is considered low, a thermal anomaly exists near the Yarmuk valley at the southern tip of the Golan Heights. New temperature measurements in the southern Golan Heights show that the distribution of the thermal anomaly is significantly wider than previously thought. The new data conforms to either a local and shallow magmatic chamber, which is in thermal steady state with the surrounding rocks, or to a transient heat front associated with localized Pleistocene magmatic intrusions in the Yarmuk. An alternative mechanism suggests that the present HF intensity is higher than the HF value calculated based on the apparent borehole temperatures due to heat removal by deep aquifer flow. A paleothermal analysis was performed using high‐resolution organic matter maturation profiles on the Late Cretaceous source rocks, across the southern Golan basin. The maturation data show remarkably similar values throughout the basin, indicating that a single thermal event led to the source rock maturation. Constraints given by geological considerations have associated the paleothermal event with Pliocene volcanic eruptions, which has allowed the calculation of the basin paleo‐heat flows, and indicated on a basin wide heat source, such as a crustal heat source. The paleothermal event is sharply bounded by a DST branching fault. This observation is suggested to be related to either strike‐slip movement associated with the DST or to heat removal and modulation by a deep hydrological system.

Abstract We present a refined map of geothermal heat flow for Antarctica, Aq1, based on multiple observables. The map is generated using a similarity detection approach by attributing observables from geophysics and geology to a large number of high‐quality heat flow values (N = 5,792) from other continents. Observables from global, continental, and regional datasets for Antarctica are used with a weighting function that allows the degree of similarity to increase with proximity and how similar the observables are. The similarity detection parameters are optimized through cross correlation. For each grid cell in Antarctica, a weighted average heat flow value and uncertainty metrics are calculated. The Aq1 model provides higher spatial resolution in comparison to previous results. High heat flow is shown in the Thwaites Glacier region, with local values over 150 mW m−2. We also map elevated values over 80 mW m−2 in Palmer Land, Marie Byrd Land, Victoria Land and Queen Mary Land. Very low heat flow is shown in the interior of Wilkes Land and Coats Land, with values under 40 mW m−2. We anticipate that the new geothermal heat flow map, Aq1, and its uncertainty bounds will find extended use in providing boundary conditions for ice sheet modeling and understanding the interactions between the cryosphere and solid Earth. The computational framework and open architecture allow for the model to be reproduced, adapted and updated with additional data, or model subsets to be output at higher resolution for regional studies.

Abstract We have successfully constructed and tested a new, portable, Hybrid Lister‐Outrigger (HyLO) probe designed to measure geothermal gradients in submarine environments. The lightweight, low‐cost probe is 1–3 m long and contains 4–12 semiconductor temperature sensors that have a temperature resolution of 0.002°C, a sample rate of 500 mbsl. Data are saved on solid‐state disks, transferred directly to the ship during deployment via a data cable, or transmitted via Bluetooth when the probe is at the sea surface. The probe contains an accelerometer to measure tilt, internal pressure, temperature, and humidity gauges. Key advantages of this probe include (1) near‐real‐time temperature measurements and data transfer; (2) a low‐cost, transportable, and lightweight design; (3) easy and rapid two‐point attachment to a gravity corer, (4) short (3–5 min) thermal response times; (5) high temporal/spatial resolution; and (6) longer deployment endurance compared to traditional methods. We successfully tested the probe both in lakes and during sea trials in May 2019 offshore Montserrat during the R/V Meteor Cruise 154/2. Probe‐measured thermal gradients were consistent with seafloor ocean‐drilling temperature measurements. Ongoing probe improvements include the addition of real‐time bottom‐camera feeds and long‐term (6–12 months) deployment for monitoring.

Abstract Geophysical and geochemical data indicate there is abundant fluid expulsion in the Nootka fault zone (NFZ) between the Juan de Fuca and Explorer plates and the Nootka continental slope. Here we combine observations from >20 years of investigations to demonstrate the nature of fluid‐flow along the NFZ, which is the seismically most active region off Vancouver Island. Seismicity reaching down to the upper mantle is linked to near‐seafloor manifestation of fluid flow through a network of faults. Along the two main fault traces, seismic reflection data imaged bright spots 100–300 m below seafloor that lie above changes in basement topography. The bright spots are conformable to sediment layering, show opposite‐to‐seafloor reflection polarity, and are associated with frequency reduction and velocity push‐down indicating the presence of gas in the sediments. Two seafloor mounds ~15 km seaward of the Nootka slope are underlain by deep, nonconformable high‐amplitude reflective zones. Measurements in the water column above one mound revealed a plume of warm water, and bottom‐video observations imaged hydrothermal vent system biota. Pore fluids from a core at this mound contain predominately microbial methane (C1) with a high proportion of ethane (C2) yielding C1/C2 ratios

Abstract We report 30 new conductive heat flow measurements collected on the Juan de Fuca plate, offshore of Grays Harbor, Washington, just seaward of the deformation front. The data were collected along Cascadia Open‐Access Seismic Transect Lines 4 and 5. A prominent basement high associated with a rift propagation pseudofault is imaged near the western end of Line 4. Lithospheric conductive cooling models, for 9 Ma oceanic crust, predict that heat flow should be ~175 mW m−2. Just seaward of the deformation front heat flow values corrected for the impact of sedimentation are ~200 mW m−2 and rapidly rise to a value of ~750 mW m−2 over the basement high. We find that (1) hydrothermal circulation redistributes heat in the Juan de Fuca plate offshore Grays Harbor, (2) heat in addition to the basal heat flux is required to fit the data, and (3) this heat likely results from a combination of fluid flow associated from ongoing hydrothermal circulation within the subducted oceanic crust and possibly with the pseudofault. Our data and modeling support previous inferences that hydrothermal circulation within the subducting oceanic crust plays an important control on plate interface temperatures.

Abstract Results from the first focused heat flow study on the U.S. Beaufort Margin provide insight into decadal‐scale Arctic Ocean temperature change and raise new questions regarding Beaufort Margin evolution. This study measured heat flow using a 3.5‐m Lister probe at 103 sites oriented along four north‐south transects perpendicular to the ~700‐km long U.S. Beaufort Margin. The new heat flow measurements, corrected both for seasonal ocean temperature fluctuations and bathymetric effects, reveal low average heat flow values (~35 mW/m2) at seafloor depths of 300–900 m below sea level (mbsl) and anomalously high (~80 mW/m2) values at seafloor depths of >1,000 mbsl, near the predicted continent‐ocean transition. Anomalously low heat flow values measured on the upper margin are consistent with previous studies suggesting decadal‐scale ocean temperature warming to ~500 mbsl. Our results, however, indicate this ocean warming likely extends to depths as great at 900 mbsl—400 m deeper than previous studies suggest—implying widespread, ongoing, methane hydrate destabilization across much of the U.S. Beaufort Margin. The cause of the anomalously high heat flow values observed at seafloor depths >1,000 at the continent‐ocean transition is unclear. We suggest three candidate processes: (1) higher heat production and lower thermal conductivity on the margin edge due to the thickest sedimentary cover at the ocean‐continent transition, (2) seaward migrating subsurface advection, and (3) possible fault‐reactivation at the northern boundary of the Alaskan Microplate.

The energy aspects of the problem of intraterrestrial heat transfer in various forms are discussed. Endogenous causes of conductive heat flow dispersion − radiogenic heat generation, tectonic movements and magmatism (volcanism), including its latent and open discharge in the form of volcanic and hydrothermal activity are considered. The geological ordering of the heat flow in the continental crust is related to convective discharge of the heat and mass flux from the mantle, marked by the isotopic composition of helium in freely circulating underground fluids. The combined transport of heat and helium, as well as the correlation of He isotopic compositions in volcanic and hydrothermal gases and Sr compositions in young lavas, testify to the silicate nature of the heat and mass flow emanating from the mantle reservoirs of different depths.

A statistical analysis of heat flow (HF) distribution along nine geotravers crossing the mid-oceanic ridges in the Atlantic, Pacific and Indian oceans is carried out. A significant asymmetry in HF distribution is established - its mean values ​​differ on opposite sides of the ridges axis. In the Earth southern hemisphere geotraverses, their western flank has a higher HF mean, and in the northern hemisphere geotraverses there is the eastern flank. Various tectonic factors that lead to such a distribution are taken into account, but the universal cause of this regularity is suggested to be the effect of the Coriolis force, which deflects the ascending magma flow in divergent zones, when the planet rotates, respectively, to the west in the southern and to the east in the northern hemispheres.