Regional Heat Flow Research Articles

Deccan Volcanism and Related Seismic Unrest in the Koyna–Warna Region, India

Abstract Koyna–Warna is a region of low-tectonic deformation and normal surface heat flow (∼40 mW/m2) in the Deccan volcanic province, India, where low-to-moderate magnitude earthquakes have continued to occur in the last 60 yr. These earthquakes are uniquely restricted to an 11×16 km2 area and confined to the upper crust between 3 and 9 km depth. Located at the last phase of the interaction of India with the Reunion mantle plume ∼65 Ma ago responsible for extensive volcanism, the cause of sustained seismicity in Koyna region is debated. Using the shear-wave velocity model derived through the joint inversion of the receiver function and surface-wave data from the seismic zone, we propose that earthquakes in the Koyna region occur due to stress concentration arising because of the high-density magma intrusions in the shallow crust at 3–9 km. The high-density mafic-ultramafic body exerts gravitationally induced stress of about ∼12 to 15 MPa. The continuation of earthquakes in the deeper part is inhibited by the possible fluid-filled mush zone imaged as a low-velocity layer at a 9–17 km depth. The magma intrusion as dike can induce a cycle of normal faulting in the overlying rock mass, as observed in the Warna region. We present the first evidence of an extremely high velocity (>4.7 km/s) layer at 40–50 km below Moho, interpreted as the presence of eclogite–peridotite responsible for producing Deccan magma in large volume.

Geothermal parameter assessment in the Southwestern Sokoto Basin, Nigeria, using spectral analysis (centroid method)

This study utilized spectral analysis (centroid method) to assess geothermal parameters in the southwestern part of the Sokoto Basin, Nigeria. The high-resolution airborne data comprised forty-nine (49) overlapping blocks, and each block was divided into 55x55 km to evaluate essential parameters such as depth to the top boundary (Zt ), centroiddepth (Zo), and magnetic source bottom (Zb = 2Zo-Zt ). The analysis revealed variable Curie points depths (CPD), ranging from 3.89 km to 26.56 km. The lowest CPD is primarily associated with basement rocks within anomalies A, B, C, D, E, F, G, H, and I, with an average CPD of 9.16 km. Furthermore, the thermal gradients ranged from 21.84 ◦C/km to 149.10 ◦C/km, with an average thermal gradient of 73.30 ◦C/km. The heat flow exhibited variations between 54.81 mW/m² and 374.24 mW/m², with average heat flow of 180.4 mW/m², indicating significant geothermal potential zones. The high thermal gradients and heat flow regions were identified, around anomalies A, B, and C. Additionally, temperature gradients identified at shallow depths ranged from 110 ◦C/km to 150 ◦C/km. The results reveal the presence of high-temperature points and anomalous geothermal potentials, particularly within anomalies A, B, and C, thus requiring further for sustainable geothermal energy generation in the study area.

REHEATFUNQ (REgional HEAT-Flow Uncertainty and aNomaly Quantification) 2.0.1: a model for regional aggregate heat flow distributions and anomaly quantification

Abstract. Surface heat flow is a geophysical variable that is affected by a complex combination of various heat generation and transport processes. The processes act on different lengths scales, from tens of meters to hundreds of kilometers. In general, it is not possible to resolve all processes due to a lack of data or modeling resources, and hence the heat flow data within a region is subject to residual fluctuations. We introduce the REgional HEAT-Flow Uncertainty and aNomaly Quantification (REHEATFUNQ) model, version 2.0.1. At its core, REHEATFUNQ uses a stochastic model for heat flow within a region, considering the aggregate heat flow to be generated by a gamma-distributed random variable. Based on this assumption, REHEATFUNQ uses Bayesian inference to (i) quantify the regional aggregate heat flow distribution (RAHFD) and (ii) estimate the strength of a given heat flow anomaly, for instance as generated by a tectonically active fault. The inference uses a prior distribution conjugate to the gamma distribution for the RAHFDs, and we compute parameters for a uninformed prior distribution from the global heat flow database by Lucazeau (2019). Through the Bayesian inference, our model is the first of its kind to consistently account for the variability in regional heat flow in the inference of spatial signals in heat flow data. Interpretation of these spatial signals and in particular their interpretation in terms of fault characteristics (particularly fault strength) form a long-standing debate within the geophysical community. We describe the components of REHEATFUNQ and perform a series of goodness-of-fit tests and synthetic resilience analyses of the model. While our analysis reveals to some degree a misfit of our idealized empirical model with real-world heat flow, it simultaneously confirms the robustness of REHEATFUNQ to these model simplifications. We conclude with an application of REHEATFUNQ to the San Andreas fault in California. Our analysis finds heat flow data in the Mojave section to be sufficient for an analysis and concludes that stochastic variability can allow for a surprisingly large fault-generated heat flow anomaly to be compatible with the data. This indicates that heat flow alone may not be a suitable quantity to address fault strength of the San Andreas fault.

Origin of high heat flow in the back-arc basins of Sumatra: An opportunity for geothermal energy development

Volcanic arcs such as the Barisan Mountains have been identified as attractive areas for the utilization of geothermal energy, as exemplified by Ulubelu in Lampung and Sarulla in North Sumatra. However, environmental factors in the Barisan Mountains remain a primary obstacle to the exploration and exploitation of geothermal energy. The back-arc basins of Sumatra exhibit the highest heat flow worldwide; however, the heat source in this area remains a controversial issue. This study aims to investigate the origin of the high heat flow in the back-arc basins of Sumatra (North, Central, and South Sumatra basins) based on geothermal data from 384 oil wells and the current literature for geological evaluation. The findings of this study indicate that the back-arc basins of Sumatra experienced severe extensional deformation during the Tertiary Period through a large pull-apart and slab rollback mechanism. This deformation resulted in the thinning of the continental crust in this region (27–32 km) and the formation of multiple normal faults. Consequently, the presence of magma resulting from mantle upwelling implies a high heat flow in the back-arc basins of Sumatra. This condition ranks the back-arc basins of Sumatra among the highest heat flow regions of the world, with heat flows >100 mW/m2. These findings indicate that the back-arc basins of Sumatra have significant opportunities to exploit their geothermal energy potential. This study provides novel insights into the potential of geothermal energy, particularly in the back-arc basins of Sumatra.

Curie point depth from airborne magnetic data analysis for geothermal exploration in southern Thailand

Southern Thailand is a high heat flow region, which implies to high-potential area of geothermal resources. Direct heat flow measurements are only available from petroleum wells in Gulf of Thailand. Therefore, indirect method of Curie Point Depth (CPD) calculation has been used to evaluate the heat flow on land of southern Thailand. CPD is the theoretical depth at which subsurface temperature reaches the value of the Curie point of magnetite, which is 578 °C. CPD can be calculated by deriving the depth of the bottom of the magnetic body to the surface using spectral analysis from airborne magnetic data, and the calculated values can produce the CPD map of southern Thailand. The results show that CPD ranges from 7.88 to 19.75 km with an average of 13.74 km, and heat flow ranges from 61.54 to 154.25 mW/m2 with an average of 90.36 mW/m2. This study suggests that the high heat flow in southern Thailand, which is higher than the regular continental crust heat flow of 65 mW/m2, is possibly caused by a high heat anomaly from mantle upwelling and expressed through weak zones of faults and sutures in extensional tectonic regimes. The high heat from mantle has elevated by five zones: (1) Ranong faults zone, (2) Khlong Marui faults zone, (3) Coastline of Surat Thani and Nakhon Si Thammarat, (4) Trang and Satun zone, and (5) Bentong-Roab suture. These five zones are considered to be high-potential areas for future geothermal resources exploration.

Deep-sourced CO2 emissions from the Eastern Himalaya Syntaxis and the Tengchong Volcanic Field, southeast Tibet

The India-Asia collision zone is believed to play a central role in Earth's geological carbon budget. The processes controlling soil CO2 flux and mechanism at this continental subduction zone margin remain however poorly constrained. Here, we focus on hydrothermal CO2 emissions from southeast Tibet, specifically from the Eastern Himalaya Syntaxis (EHS) and the Tengchong Volcanic Field (TVF), with the twin goals of informing models of carbon cycling and ascertaining the source of hydrothermal degassing systems. In-situ measurements of soil CO2 flux from the Aqiong, Caquka, Nongchaka, Rongduo, and Woka hydrothermal fields of the EHS yield average soil CO2 fluxes of 72, 5, 13, 66, and 10 g m−2 day−1, respectively. Regional heat flow, tectonic regimes, and CO2 content in the spring gas are plausible controlling factors for soil CO2 flux, which is crucial to quantifying total CO2 output in continental collision zones. The compositions and He-C-N isotopes of hydrothermal volatiles from two study regions are reported here as well. Analysis of the He-C-N isotopes in terms of distances to the Jiali fault and the nearest Holocene volcano confirms that the Jiali fault and Holocene volcanoes have a significant impact on discharging deep-sourced CO2 from the EHS and TVF hydrothermal systems to the surface. The 3He/4He values of EHS hydrothermal volatiles (92 to 98°E), combined with previous data (82 to 92°E), show a clear increasing trend from south to north. Thus, we propose an updated model of enriched mantle wedge source for the EHS hydrothermal volatiles, based on multi-component mixing calculations of the He-CO2 systematics. The EHS hydrothermal volatiles exhibit systematics spatial variations from the core location to the bilateral segments, suggesting the highest 3He/4He ratio and carbonate-rich characteristics at the core location possibly controlled by the asthenosphere upwelling caused by the deep fragmentation structure.

Thin Ice Lithospheres and High Heat Flows on Europa From Large Impact Structure Ring‐Graben

AbstractCraters are probes of planetary surface and interior properties. Here we measure depths, widths, and spacing of circumferential ring‐graben surrounding the two largest multiring impact structures on Europa, Tyre and Callanish. We estimate formation conditions including the ice shell structure. The radial extension necessary to form these graben is thought to be caused by asthenospheric drag of warmer, more ductile ice and/or water flowing toward the excavated center of the crater, under a brittle‐elastic lithospheric lid. Measurements of graben depths from stereo‐photoclinometric digital elevation models result in estimates of displacement, strain, and stress experienced by the ice shell. Graben widths are used to estimate the intersection depth of the bounding normal faults, a quantity related to the brittle‐ductile transition depth that approximates elastic shell thickness during crater collapse. Heat flows at the time of crater formation as well as ice lithosphere and total shell thickness are thus also constrained. Average widths and depths tend to decrease with increasing distance from the structure center, while inter‐graben spacing generally increases. Varied assumptions yield plausible total conductive ice shell thickness estimates between 4–8 and 2.5–5 km for Tyre and Callanish, respectively, and heat flows of ∼70–115 (±30) mW m−2 for realistic thermal conductivities, consistent with other geophysical estimates for Europa. Higher heat flows are consistent with thin (≲10 km), conductive ice shells and impact breaching, or penetration of the stagnant lid for a convecting ice shell. Callanish, geologically younger, formed in a time or region of greater heat flow than Tyre.

New heat flow data on the South Balearic margin: Evidence of regional fluid circulation system

Crustal heat loss processes in contexts other than mid-ocean ridge flanks are still poorly understood and described in the literature. In this work, we present 54 new surface heat flow measurements recorded along the South Balearic margin and across the Hannibal High area, in the Western Mediterranean Sea, away from spreading centres. The South Balearic margin is a narrow continental margin expressed on the seabed topography by the steep Emile Baudot Escarpment while the Hannibal High area, further south, is a presumed volcanic oceanic crust zone. Recent heat flow studies pointed out the presence of strong local thermal anomalies, imprinted in regional deep basin heat flow increasing from the eastern to the western Algerian basins (70–90 to 100–130 mW/m2). The new data in this study confirm local anomalies around the Emile Baudot seamounts and allow the delineation of some low and high heat zones. We show that (1) a correlation exists between the heat flow variability and the sedimentary cover thickness, and (2) the most pronounced anomaly is a low heat flow zone (30 km wide) observed in the mid-slope South Formentera basin, close to the basaltic basement of the Los Martines volcano. The correlation of heat flow with sedimentary thickness, the lateral extent of the heat flow anomalies, the flux peak magnitudes, and the co-existence of both low and high anomalies suggest the presence of an active fluid circulation system. Based on the arrangement of the anomalies in relation to the basaltic basement seamounts, we consider a syphon-type circulation system in the Formentera basin. Reduced heat flow suggests a recharge zone close to the Los Martines seamount, while local high heat flow located close to a smaller seamount could be a potential zone of fluid discharge. Although different buoyancy-driven circulations could occur in the South Balearic margin, we believe that a syphon-type hydrothermal circulation along permeable basaltic mounds and sealed basement conduits, similar to the off-axis oceanic crust, is best developed in the young marginal basin of the South Balearic margin.

Experimental and numerical study of zonal heat and moisture migration inside artificial ice rinks

Ice rinks feature typical non-uniform indoor environment with evident vertical and horizontal parameter differences. A validated CFD model established based on the on-site measurement is utilized to investigate the indoor environment along with the zonal heat and moisture transfer characteristics in a recreational ice rink. It is demonstrated that there are both cooling and heating demands inside the ice hall due to different control standards for various functional regions. Zonal mixing induces a large amount of additional load with 53.5% of the heat brought by the dehumidifiers eventually flowing into the ice sheet and carried away by the refrigeration system. The ice sheet cooperates with the dehumidifiers to dislodge the indoor moisture gain. The importance of proper design of ventilation systems and adequate physical separation is emphasized. Zonal migration coefficients are proposed, and the variation range influenced by different factors are investigated. The migration coefficients between the near-ice zone and the occupied ice field are around 4 W/(m2·K) and 5 g/(s·m2), and those between the occupied and unoccupied ice field are around 14 W/(m2·K) and 18 g/(s·m2). The findings provide a simplified calculation method for regional heat and moisture flow, and are beneficial for the optimization of system design and energy conservation in ice rinks.

Granitoids indicating moderate to high heat production associated with oceanic subduction system in the NE Tibetan Plateau

Regional heat flow provides a direct surface indication of the thermal state and energy balance of the lithosphere. Heat flux in the Tibetan Plateau remains poorly studied due to the lack of adequate information on heat flow. In this study, we investigated granitoids from the Gonghe-Guide district located in the NE Tibetan Plateau, which have important significance as hot and dry rocks with potential for geothermal resources. Samples from granitoid rocks as well as felsic dikes were collected from this area, and their geochemical data were combined with regional geophysical and drilling core data to evaluate a high-heat-flow anomaly. Our data show that granitoid rocks, including granodiorite, monzogranite, and syenogranite, crystallized at ca. 253−240 Ma, while felsic dikes formed ca. 230 Ma. The former were emplaced during the oceanic subduction process, whereas the latter formed in the syncollisional stage associated with the closure of the paleo-Zongwulong Ocean. Geochemically, these granitoid rocks are metaluminous to slightly peraluminous, with an average differentiation index (DI) value of 80, and they are classified as weakly to moderately fractionated I-type granites. The felsic dikes are peraluminous with high DI values (average of 95), typical of highly fractionated I-type granites. In terms of their high K and especially U and Th abundances, the calculated radioactive heat generation produced by the granodiorite, monzogranite, syenogranite, and felsic dikes is 1.85, 2.91, 6.85, and 3.02 μW/m3, respectively. Their moderate to high heat production generates a local heat-flow anomaly of 14.8−22.2 mW/m2 above the regional value of subduction zones, accounting for 11%−18% of the total regional heat flow. In combination with regional magnetotelluric data, the high-heat-flow anomaly may be attributed to an additional heat-flow contribution from a partial melt layer beneath this region. Furthermore, there is a significant positive correlation between the radioactive heat generation and magmatic fractionation, indicating that the enrichments of heat-producing elements are controlled by fractional crystallization and subsequently source composition. The granitoid rocks with high heat generation correspond to the large-scale intermediate-felsic magmatism during the subduction stage. We propose a model wherein a continuous subduction process during the closure of the paleo-Zongwulong Ocean and protracted cooling and crystallization processes resulted in the enrichment in heat-producing elements.

Experimental Study on Spray Cooling Heat Transfer of LN2 for a Large Area

Spray cooling has been considered one of the most promising thermal control methods of high-heat flux devices. Most of the spray cooling research focuses on electronic components as the main application object to achieve higher heat dissipation heat flow in ambient temperature regions for small areas. Water is the most common cooling medium. This paper investigates the application of spray cooling thermal control over large areas. In this study, the heat-transfer characteristics of liquid nitrogen (LN2) for large areas was investigated by conducting experiments. The test surface is 500 mm × 500 mm, which was cooled by a nine-nozzle array. The spray nozzles used in the experiment were conical nozzles with an orifice diameter of 1.6 mm, a spray angle of 120°, and a spray height of 42 mm. Liquid nitrogen was forcefully ejected from nozzles by the high pressure of a liquid storage tank to cool the test surface. According to the cooled surfaces, spray directions, and spray pressures, three groups of experiments were conducted. The results showed that the smooth flat surface has the best heat-transfer performance in three kinds of surface structures, which are macro surface, porous surface, and smooth flat surface. The heat-transfer coefficient varied by ±20% with different spray directions, and the surface heat-transfer coefficient increased linearly with increasing spray pressure. Most of the spray cooling research focuses on heat dissipation in the ambient temperature region for equipment over small areas. The results can benefit thermal control application in various fields. The research in this paper can provide a reference for the application of large-area spray cooling, and the application areas mainly include metal manufacturing processing cooling, aircraft skin infrared radiation characteristics modulation, and laser weapon equipment cooling.

Strong Variability in the Thermal Structure of Tibetan Lithosphere

AbstractWe present a model of thermal lithospheric thickness (the depth where the geotherm reaches a temperature of 1300°C) and surface heat flow in Tibet and adjacent regions based on a new thermal‐isostasy method. The method accounts for crustal density heterogeneity, is free from any assumption of a steady‐state lithosphere thermal regime, and assumes that deviations from crustal Airy‐type isostasy are caused by lithosphere thermal heterogeneity. We observe a highly variable lithospheric thermal structure which we interpret as representing longitudinal variations in the northern extent of the subducting Indian plate, southward subduction of the Asian plate beneath central Tibet, and possible preservation of fragmented Tethyan paleo‐slabs. Cratonic‐type cold and thick lithosphere (200–240 km) with a predicted surface heat flow of 40–50 mW/m2 typifies the Tarim Craton, the northwest Yangtze Craton, and most of the Lhasa Block that is likely refrigerated by underthrusting Indian lithosphere. We identify a “North Tibet anomaly” with thin (<80 km) lithosphere and high surface heat flow (>80–100 mW/m2). We interpret this anomaly as the result of removal of lithospheric mantle and asthenospheric upwelling at the junction of the Indian and Asian slabs with opposite subduction polarities. Other parts of Tibet typically have intermediate lithosphere thickness of 120–160 km and a surface heat flow of 45–60 mW/m2, with patchy anomalies in eastern Tibet. While different uplift mechanisms for Tibet predict different lithospheric thermal regimes, our results in terms of a highly variable thermal structure beneath Tibet suggest that topographic uplift is caused by an interplay of several mechanisms.

The Potential of Sukadana Basalt Province as a New Geothermal Resources in The Back Arc of Sumatra

Geothermal resources are currently obtained from areas within volcanic arcs, such as the Pertamina Ulu Belu and Supreme Energy Rajabasa Geothermal Fields. However, this understanding may change in the future, as the Quaternary Sukadana Basalt Province (SBP), located in the back arc, is believed to have potential as a future geothermal energy resource. This research aims to explore the various factors that contribute to the high heat flow in the SBP region and generate a new perspective on geothermal energy particularly in the Lampung province. The methods used integrate previous research findings, such as heat flow data, regional tectonics, and geological structures, with new petrography-whole rock geochemistry. The whole rock geochemistry was determined using X-Ray Fluorescence (XRF), Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The SBP was formed by the Paleogene northwest-southeast striking fault and influenced by the Quaternary northeast-southwest striking fault, which may serve as conduits for hydrothermal fluid in addition to their vesicular structures. Geochemical analysis suggests the presence of both mantle plume and subduction-related processes. The magmatism linked to subduction-plume tectonic mechanisms and the thinning of the crust due to pull-apart motion caused by the movement of two large faults (Sumatra Fault Zone and Bangka Shear) can increase regional heat flow to 100±10 mW/m2. As a result, the SBP has significant potential as a source of geothermal energy for electricity generation in the future.

Imaging the magmatic plumbing of the Clear Lake Volcanic Field using 3-D gravity inversions

The Quaternary Clear Lake Volcanic Field (CLVF) in the Northern California Coast Range is the youngest of a string of northward-younging volcanic centers in the state. The CLVF is located within the broad San Andreas Transform Fault System and has been active intermittently for ∼2 million years. Heat beneath the CLVF supports The Geysers, one of the largest producing geothermal fields in the world.Previous geophysical studies proposed the existence of a magma reservoir beneath Mount Hannah, which is northeast of The Geysers, near the geographic center of the CLVF. The lateral extent, depth, and presence of melt within this reservoir are poorly constrained, as is the relationship between this body and the broader magmatic plumbing of the CLVF. To gain a clearer and more comprehensive picture of the CLVF magma source region, a gravity dataset was compiled and the first 3-D gravity inversions of the CLVF were completed.Field and synthetic model inversions from the current study both indicate that the gravity low roughly centered on Mount Hannah is not accurately explained by a 5–7 km thick lens of Mesozoic Great Valley Sequence (ρ=2.58g/cm3) as proposed by Stanley et al. (1998). The observed gravity low is more accurately described by one or more silicic, partial melt bodies between The Geysers and Mount Hannah. Although our inversions cannot constrain the exact depth and geometry of these bodies, the recovered models indicate the existence of a partial melt zone between 6 and 13 km depth.The prolonged eruption history of the CLVF, coupled with the compositional variation of erupted rocks over time and space, is consistent with the existence of several, potentially ephemeral, melt-bearing bodies as opposed to one large melt body. Given the density and location of the recovered anomaly, rhyolite-MELTS thermodynamic modeling suggests the existence of 10–30% rhyodacitic melt within the proposed silicic magma reservoir at about 700 °C and 8 km depth (210 MPa). Independent petrologic, geochemical, and seismic evidence indicates that this silicic partial melt zone is underlain by basaltic melt in the lower to middle crust (13 to 21 km depth), which is fed by a mantle source.Eruptions in the past ∼8.5–13.5 thousand years; high regional heat flow; 3He enrichment of hydrothermal fluids; and our modeling, which suggests the presence of a mid-crustal, silicic partial melt zone, point to a still-active CLVF. The relatively low estimates of partial melt (10–30%) predicted by thermodynamic modeling indicates that an injection of new magma into the imaged partial melt zone is needed to generate sufficient melt to incite future eruptions. Despite the low percent melt estimates within the proposed silicic partial melt zone the potential for future volcanic eruption remains. Due to the proximity of the CLVF to cities surrounding Clear Lake and the densely populated San Francisco Bay Area, continued research and monitoring of the volcanic field are warranted. The geophysical and petrologic modeling presented here improves our understanding of the CLVF magma plumbing system and allows us to better characterize its associated volcanic hazards.

Formation of the hydrothermal system from granite reservoir for power generation in igneous rock areas of South China

Hydrothermal systems occurring in granite reservoir widely exist over the world, but those can continuously supply large quantities of hot water with certain temperature for power generation are rare, e.g., TangKeng geothermal system in South China. It is unclear how the granite reservoir keeps this kind of large natural yield of geothermal water with stable temperature and the genesis study is of great importance to find similar geothermal fields for further exploitation. This paper aims to discuss the formation of TangKeng geothermal system in granite of Cretaceous period, with emphasis on heat sources, geothermal fluid circulation and reservoir temperature. Results show that average regional heat flow of 72.2 mW/m2 is composed by almost equal contribution from heat production of radioactive elements in crust and conductive heat of mantle. Extension and thinning processes of lithosphere and upwelling of magma in the asthenosphere caused the thermal erosion of the upper mantle and lower crust but doesn't induce the formation of magma chamber or partial molten in the upper crust and had very limited influences on the regional thermal state. Heat flow of the crust is mainly composed by intrusive granite pluton with high heat production value in the surface and the felsic upper crust. Geothermal fluid is recharged by the local precipitation from the surrounding mountains through regional developed NE and NW faults system. The crushed fine-middle grained biotite granite or granite with fractures and fissures of Mesozoic period provide excellent reservoir for water circulation. Interactions between regional faults and fractures in granites provide excellent conduits for additional recharge from shallow groundwater which is continuously recharged by the Rong Jiang River water during the ascending process. Reservoir temperature is calculated to be about 140–143 °C with correction of slightly CO2 degassing and mixing. Missing of caprock for most of the areas and mixing with cold groundwater during ascending process led to the occurrence of geothermal water with lower temperature of 92 °C collected at the surface.Fractured granite reservoir with high heat productivity from radioactive elements, well developed NE and NW oriented faults system and continuous recharge from local precipitation and surface water nearby are essential for the formation of this kind of hydrothermal system.

Geochemistry of oils and condensates from the lower Eagle Ford formation, South Texas. Part 3: Basin modeling

Maturity-dependent bulk properties and molecular compositions of oils and condensates produced from the lower Eagle Ford shales exhibit two distinct regional trends with production depth. Samples west of 98.6 West longitude form a trend that is offset upwardly by ∼2000 ft compared to samples near the Karnes Trough area. This offset is unlikely due to variations in source facies or regional heat flow. To test whether the offset is the result of different amounts of uplift and overburden removal, a psuedo 3D basin model was constructed for the Eagle Ford Formation using standard geologic methods and rock-calibrated 1D burial histories. Present-day thermal maturity was found to correlate with reconstructed maximum burial depth (MBD). When maturity-dependent geochemical parameters are plotted versus MBD, the trends show significantly greater fidelity than when plotted versus true vertical depth; however, the regional offsets are still evident, suggesting that the basin model could be refined. Petroleum samples can be used to calibrate basin models provided they reflect the current maturity of their source. This criterium may be met by unconventional fluids provided the producing strata is charged with the latest generated hydrocarbons from very limited, localized fetch area – conditions believed to be present in the lower Eagle Ford. API gravity from initial production, the only oil property reported for all wells, generally correlates with molecular maturity parameters but can be influenced by other processes. To compensate for these extraneous influences, trends of API gravity versus TVD were plotted for 0.2° longitudinal segments across the Eagle Ford play and used to model the relative amount of uplift and erosion needed to yield oil with the same API gravity and by inference the same maturity. Calculated MDB's from the API gravity oil-based model were found to agree well with those determined by the rock-based basin model and yielded more coherent depth trends with the measured maturity parameters. Both the rock-based and oil-based models find that the amount of Neogene uplift and overburden removal to be no more than ∼500 ft in the area near the San Marcos Arch and increases to the west, reaching ∼6500 ft in Maverick County. This finding strongly supports, if not proves, Cander's (2013) model for petroleum retention/production in the Eagle Ford shales and that the produced petroleum is a near-instantaneous, rather than a cumulative charge, of the latest generated hydrocarbons. This implies that unconventional continuous source petroleum systems are suitable for oil-based calibration of basin models. In many ways, the Eagle Ford petroleum system is ideal in its simplicity for the application of type of calibration.

Surface heat flow measurements in the eastern margin of the Japan Sea using a 15 m long geothermal probe to overcome large bottom-water temperature fluctuations

Accurate surface heat flow data are required for a wide range of geological and geophysical applications. However, sediment temperature measurements beneath the seafloor often involve large uncertainties owing to the influence of bottom-water temperature (BWT) fluctuations. Previous studies reported apparently negative geothermal gradients in the Joetsu Basin of the Japan Sea and suggested that BWT fluctuations disturbed sediment temperatures. To address this problem, we monitored BWTs in the Joetsu Basin over a 2 year period to determine the depth at which the influence of BWT fluctuations on sediment temperature becomes negligible. Combined with sediment thermal diffusivity data, we determined that the BWT fluctuations can disturb sediment temperatures to a depth of 2 m. We obtained heat flow values of 81–88 mW m− 2 by measuring sediment temperatures at depths > 2 m using a 15 m long geothermal probe. The measured heat flow values are inversely correlated with topography owing to the effect of topographic change on the geothermal structure near the seafloor. A two-dimensional geothermal structure model was constructed to account for the topography, yielding an estimated regional background heat flow of 85 ± 6 mW m− 2. This study provides two important guidelines for obtaining accurate surface heat flow data in marine areas with large-amplitude BWT fluctuations: (1) quantitative information regarding BWT fluctuations and sediment thermal diffusivity is required to evaluate the depth range to which BWT fluctuations affect sediment temperature; and (2) information regarding the lithology and consolidation state of seafloor sediments is required for effective penetration using a long probe.

Anomalously High Heat Flow Regions Beneath the Transantarctic Mountains and Wilkes Subglacial Basin in East Antarctica Inferred From Curie Depth

AbstractThe Transantarctic Mountains (TAMs) separate the warmer lithosphere of the Cretaceous‐Tertiary West Antarctic rift system and the colder and older provinces of East Antarctica. Low velocity zones beneath the TAM imaged in recent seismological studies have been interpreted as warm low‐density mantle material, suggesting a strong contribution of thermal support to the uplift of the TAM. We present new Curie Point Depth (CPD) and geothermal heat flow (GHF) maps of the northern TAM and adjacent Wilkes Subglacial Basin (WSB) based exclusively on high resolution magnetic airborne measurements. We find shallow CPD and high GHF beneath the northern TAM, reinforcing the hypothesis of thermal support of the topography of the mountain range. Additionally, this study demonstrates, that limiting spectral analysis to areas with a high density of aeromagnetic measurements increases the resolution of CPD estimates revealing localized shallow CPD and associated high heat flow in the Central Basin of the WSB and the Rennick Graben (RG). Across the study area the CPD ranges from 15 to 35 km and the GHF values range from 30 to 110 mW/m2. The recovered CPD range is compatible with recent Moho depth estimates, as the CPD predominantly lies within the crust, rather than in the magnetite‐poor mantle. GHF estimates, based on the CPD estimates, show a good agreement to sparse in situ GHF measurements and the location of active volcanoes. Comparison to existing continent‐wide GHF estimates shows strong differences from magnetically‐derived heat flow estimates, while seismologically‐derived heat flow estimates show the best agreement to our results.

Characteristics of Radiogenic Heat Production of Widely Distributed Granitoids in Western Sichuan, Southeast Tibetan Plateau

Abstract Investigating the genesis of geothermal resources requires a thorough understanding of the heat source mechanism, which is also a vital basis for the efficient exploration and utilization of geothermal resources. Situated in the eastern Himalayan syntax, western Sichuan is considered to be one of the main concentration regions of high-temperature geothermal resources in China. To date, various studies have been carried out to reveal the heat source and genesis of the abundant high-temperature resources in this area; however, studies on the contribution of the radioactive heat generated by the widely distributed granitoids to the high-temperature geothermal resources remain scarce. In order to resolve this knowledge gap, we attempted to obtain evidence from the geochemical data published in the literature in the past few decades. A total of 548 radiogenic heat production rate data were determined. The statistical data indicate that the average concentrations of the heat-producing elements U, Th, and K are 6.09±5.22 ppm, 26.74±16.78 ppm, and 3.51±0.82%, respectively. The calculated heat production values of the granitoids vary from 0.52 to 10.86 μW/m3, yielding an arithmetic average value of 3.74±2.15 μW/m3, which is higher than that of global Mesozoic–Cenozoic granites (3.09±1.62 μW/m3). Based on the heat production values, the capacity of the granitic batholiths to store heat was assessed, and the Dongcuo pluton was found to be the largest heat reservoir (382.88×1013 J/a). The distribution of the crustal heat flow was examined using the calculated heat production data and the stratigraphic structure obtained via deep seismic sounding in the study area. The results indicate that the crustal heat flow is 48.3–56.2 mW/m2, which is mainly contributed by the radioactive decay in the granitoids in the upper crust. The fact that it accounts for nearly half of the regional background heat flow indicates that the radiogenic heat from the granitoids is an important heat source for the formation of the thermal anomaly and the high-temperature geothermal resources in the study area. Thus, the results obtained in this study highlight the importance of the widely distributed granitoids to high-temperature geothermal resources in western Sichuan.

A geothermal heat flow model of Africa based on random forest regression

Geothermal heat flow (GHF) data measured directly from boreholes are sparse. Purely physics-based models for geothermal heat flow prediction require various simplifications and are feasible only for few geophysical observables. Thus, data-driven multi-observable approaches need to be explored for continental-scale models. In this study, we generate a geothermal heat flow model over Africa using random forest regression, originally based on sixteen different geophysical and geological quantities. Due to an intrinsic importance ranking of the observables, the number of observables used for the final GHF model has been reduced to eleven (among them are Moho depth, Curie temperature depth, gravity anomalies, topography, and seismic wave velocities). The training of the random forest is based on direct heat flow measurements collected in the compilation of (Lucazeau et al., Geochem. Geophys. Geosyst. 2019, 20, 4001–4024). The final model reveals structures that are consistent with existing regional geothermal heat flow information. It is interpreted with respect to the tectonic setup of Africa, and the influence of the selection of training data and observables is discussed.