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The Eastern Cordillera of the Colombian Andes is a high-elevation asymmetric plateau subjected to NW–SE shortening. An interesting aspect of this plateau is the presence of high geothermal gradients (up to 52 °C/km), constrained by wells drilled in sedimentary basins. Radial and transverse receiver functions were computed at key sites in the plateau and the adjacent low-elevation foreland region to better understand the controlling factors of these anomalous gradients. Results indicate the presence of tilted anisotropic layers in the uppermost crust of the Cordillera, and nonexistent to weak anisotropy in the foreland region. The estimated SE fast-axis trend of the anisotropy is related to NNE-striking faults and top-to-the-east tectonic transport during deformation. We interpret the SE fast axis as being associated with shearing of NW-dipping faults in the plateau. Compiled thermochronological data point to high deformation and exhumation rates since the middle Miocene, which we use to propose that the rapid rise of deep and hot blocks along major regional faults is perturbing the background geothermal gradient. Regions near major thrust faults in the Eastern Cordillera are potential areas for geothermal energy exploration due to the perturbed geothermal gradient and enhanced fluid infiltration related to deep fault systems.

The Sulawesi Sea and Sulawesi Island are located in the western Pacific area where volcanic activity, plate subduction, and seismic activity are very active. The Sulawesi basin formed during the Middle Eocene-Late Eocene and nearly half of the Eocene oceanic crust has subducted below the North Sulawesi Trench. The Sulawesi Island was spliced and finalized in the Early Pliocene-Pleistocene during volcanic activity and is recently very active. This area is an optimal location to study volcanic geothermal conditions and subduction initiation mechanisms in the southern part of the western Pacific plate margin, which are important in geothermal and geodynamic research. In this study, we combined 133 heat flow data with gravity and magnetic data to calculate the Moho structure and Curie point depth of the Sulawesi Sea and periphery of the Sulawesi Island, and analyze the distribution characteristics of the geothermal gradient and thermal conductivity. The results show that the average depths of the Moho and Curie surfaces in this area are 18.4 and 14.3 km, respectively, which is consistent with the crustal velocity layer structure in the Sulawesi Basin previously determined by seismic refraction. The average geothermal gradient is 4.96°C (100 m) −1 . The oceanic area shows a high geothermal gradient and low thermal conductivity, whereas the land area shows a low geothermal gradient and high thermal conductivity, both of which are consistent with statistical results of the geothermal gradient at the measured heat flow points. The highest geothermal gradient zone occurs in the transition zone from the Sulawesi Sea to Sulawesi Island, corresponding to the spreading ridge of the southward-moving Sulawesi Basin. Comprehensive gravity, magnetic, and geothermal studies have shown a high crustal geothermal gradient in the study area, which is conducive to the subduction initiation. The northern part of the Palu-koro fault on the western side of Sulawesi is likely the location where subduction initiation is occurring. During the process of moving northwest, the northern and eastern branches of Sulawesi Island have different speeds; the former is slow and the latter is fast. These branches also show different deep tectonic dynamic directions; the northern branch tilts north-up and the eastern branch tilts north-down.

The present study analyzes available aeromagnetic and recently acquired ground gravity data to understand geothermal gradients covering parts of northeastern India. The scaled spectral analysis of aeromagnetic data has been adopted for computing the bottom magnetic interface depths that help to estimate geothermal source beneath thrust and fold belts. The database indicates that high geothermal gradients observed in northwestern part of the study area encompass uplifted Shillong Plateau and thrust belts. The geothermal gradients are gradually decreasing towards eastern portion of Inner Fold Belts comprising northern fringe of Indo-Burmese Ranges. An elliptical-shaped northeast-trending conspicuous high aeromagnetic anomaly zone coincides with gravity signature of high density mafic/ultramafic rocks that may correspond to carbonatite complex, which are potential host for rare earth elements (REE) mineralization. An attempt has been made to comprehend the relation between crustal lateral heterogeneities of aeromagnetic and gravity interfaces and subsurface structures, in conjunction with the nature of deformation and seismic characteristics of northeast India. The estimated Euler depth solutions and modelling results of gravity and aeromagnetic data reveal that substantial crustal heterogeneities in the form of mafic intrusions or underplating beneath Shillong Plateau and Indo-Burmese arc display higher seismicity. The high anomalous geothermal gradients coincide with mafic intrusive or underplated rocks beneath Shillong Plateau and thrust belts that may act as potential geothermal reservoir. Research highlights High geothermal gradients observed in northwestern part of the study area covering uplifted Shillong Plateau and thrust belts. The results of geothermal gradient beneath thrust and fold belts of NE India vary between 14 and 22°C/km and the heat flow values are varying from 34 to 56 mW/m 2 . The conspicuous high aeromagnetic anomaly upheld with gravity signature of high density mafic/ultramafic rocks may be associated with carbonatite complex. The present study established the relation between the crustal lateral heterogeneities of aeromagnetic–gravity interface depths and seismic characteristics of NE India.

Geothermal gradients and present day heat flow values were evaluated for about seventy one wells in parts of the eastern Niger delta, using reservoir and corrected bottom-hole temperatures data and other data collected from the wells. The results showed that the geothermal gradients in the shallow/continental sections in the Niger delta vary between 10 - 18° C/km onshore, increasing to about 24° C/km seawards, southwards and eastwards. In the deeper (marine/paralic) section, geothermal gradients vary between 18 - 45° C/km. Heat flow values computed using Petromod 1-D modeling software and calibrated against corrected BHT and reservoir temperatures suggests that heat flow variations in this part of the Niger delta range from 29-55 mW/m2 (0.69-1.31 HFU) with an average value of 42.5 mW/m2 (1.00 HFU). Heat flow variations in the eastern Niger delta correspond closely to variations in geothermal gradients. Geothermal gradients increase eastwards, northwards and seawards from the coastal swamp. Vertically, thermal gradients in the Niger delta show a continuous and non-linear relationship with depth, increasing with diminishing sand percentages. As sand percentages decrease eastwards and seawards, thermal gradient increases. Lower heat flow values (< 40 mW/m2) occur in the western and north central parts of the study area. Higher heat flow values (40 - 55 mW/m2) occur in the eastern and northwestern parts of the study area. A significant regional trend of eastward increase in heat flow is observed in the area. Other regional heat flow trends includes; an eastwards and westwards increase in heat flow from the central parts of the central swamp and an increase in heat flow from the western parts of the coastal swamp to the shallow offshore. Vertical and lateral variations in thermal gradients and heat flow values in parts of the eastern Niger delta are influenced by certain mechanisms and geological factors which include lithological variations, variations in basement heat flow, temporal changes in thermal gradients and heat flow, related to thicker sedmentary sequence, prior to erosion and evidenced by unconformities, fluid redistribution by migration of fluids and different scales of fluid migration in the sub-surface and overpressures. Copyright 2016 Geological Society of India

On the contemporary Earth, distinct plate tectonic settings are characterized by differences in heat flow that are recorded in metamorphic rocks as differences in apparent thermal gradients. In this study we compile thermal gradients [defined as temperature/pressure (T/P) at the metamorphic peak] and ages of metamorphism (defined as the timing of the metamorphic peak) for 456 localities from the Eoarchean to Cenozoic Eras to test the null hypothesis that thermal gradients of metamorphism through time did not vary outside of the range expected for each of these distinct plate tectonic settings. Based on thermal gradients, metamorphic rocks are classified into three natural groups: high dT/dP [>775°C/GPa, mean ∼1110°C/GPa (n = 199) rates], intermediate dT/dP [775-375°C/GPa, mean ∼575°C/GPa (n = 127)], and low dT/dP [<375°C/GPa, mean ∼255°C/GPa (n = 130)] metamorphism. Plots of T, P, and T/P against age demonstrate the widespread occurrence of two contrasting types of metamorphism-high dT/dP and intermediate dT/dP-in the rock record by the Neoarchean, the widespread occurrence of low dT/dP metamorphism in the rock record by the end of the Neoproterozoic, and a maximum in the thermal gradients for high dT/dP metamorphism during the period 2.3 to 0.85 Ga. These observations falsify the null hypothesis and support the alternative hypothesis that changes in thermal gradients evident in the metamorphic rock record were related to changes in geodynamic regime. Based on the observed secular changes, we postulate that the Earth has evolved through three geodynamic cycles since the Mesoarchean and has just entered a fourth. Cycle I began with the widespread appearance of paired metamorphism in the rock record, which was coeval with the amalgamation of widely dispersed blocks of protocontinental lithosphere into supercratons, and was terminated by the progressive fragmentation of the supercratons into protocontinents during the Siderian-Rhyacian (2.5 to 2.05 Ga). Cycle II commenced with the progressive reamalgamation of these protocontinents into the supercontinent Columbia and extended until the breakup of the supercontinent Rodinia in the Tonian (1.0 to 0.72 Ga). Thermal gradients of high dT/dP metamorphism rose around 2.3 Ga leading to a thermal maximum in the mid-Mesoproterozoic, reflecting insulation of the mantle beneath the quasi-integral continental lithosphere of Columbia, prior to the geographical reorganization of Columbia into Rodinia. This cycle coincides with the age span of most anorogenic magmatism on Earth and a scarcity of passive margins in the geological record. Intriguingly, the volume of preserved continental crust of Mesoproterozoic age is low relative to the Paleoproterozoic and Neoproterozoic Eras. These features are consistent with a relatively stable association of continental lithosphere between the assembly of Columbia and the breakup of Rodinia. The transition to Cycle III during the Tonian is marked by a steep decline in the thermal gradients of high dT/dP metamorphism to their lowest value and the appearance of low dT/dP metamorphism in the rock record. Again, thermal gradients for high dT/dP metamorphism show a rise to a peak at the end of the Variscides during the formation of Pangea, before another steep decline associated with the breakup of Pangea and the start of a fourth cycle at ca. 0.175 Ga. Although the mechanism by which subduction started and plate boundaries evolved remains uncertain, based on the widespread record of paired metamorphism in the Neoarchean we posit that plate tectonics was established globally during the late Mesoarchean. During the Neoproterozoic there was a change to deep subduction and colder thermal gradients, features characteristic of the modern plate tectonic regime.

Oceanic lithosphere is generated at divergent plate boundaries and disappears at convergent plate boundaries. Seafloor spreading and plate subduction together constitute the physical coupling and mass conservation relationships to the movement of lithospheres on Earth. Subduction zones are a key site for the transfer of both matter and energy at converging plate boundaries, and their study has been the hot spot and frontier of Earth system science since the development of plate tectonics theory. As far as the dynamic regime and geothermal gradient of convergent plate margins are concerned, they have different properties in different stages of the subduction zone evolution. In general, the early low-angle subduction leads to compressional tectonism dominated by low geothermal gradients at the plate interface, and the late high-angle subduction results in extensional tectonism dominated by high geothermal gradients at the plate interface and its hanging wall. Active rifts are produced along suture zones through not only slab rollback or slab breakoff in the terminal stage of oceanic subduction but also foundering and thinning of the lithosphere in the post-subduction stage. Due to the differences and changes in the geometric and thermobaric structures of convergent plate margins, a series of changes in the type of metamorphism and magmatism can occur in active and fossil subduction zones. Dehydration and melting of the subducting oceanic crust are prominent at subarc depths, giving rise to fluids that dissolve different concentrations of fluid-mobile incompatible elements. The subduction zone fluids at subarc depths would chemically react with the overlying mantle wedge peridotite, generating metasomatites as the mantle sources of mafic magmas in oceanic and continental arcs. However, these metasomatites did not partially melt immediately upon the fluid metasomatism to trigger arc magmatism, and they did not melt until they were heated by asthenospheric convection due to rollback of the subducting slab. Therefore, recognition of the changes in the dynamic regime and geothermal gradient of subduction zones in different stages of plate convergence not only provides insights into geodynamic mechanisms of the tectonic evolution from subduction zones to orogenic belts, but also places constraints on the formation and evolution of different types of metamorphic and magmatic rocks within the advanced framework of plate tectonics.

High‐temperature geothermal areas are often characterized by widespread surficial manifestations, whose location is strictly controlled by sets of faults of regional relevance. The geochemical and isotopic signature of the discharged fluids can reveal key information on the geothermal fluids pathway, shedding light on the sources and fluid‐rock interaction within the geothermal reservoirs. In this paper, a geochemical and structural data set from the Larderello geothermal area and surroundings is presented and discussed. We constrain the role of transfer and normal faults in controlling the geothermal circulation enhanced by a cooling magmatic intrusion underneath the Lago area (SW of Larderello). The structural control on the fluids circulation is highlighted by both the location of the CO2 emissions along the fault segments, where permeability is enhanced, and their degassing rates, which increase moving away from the core of the Larderello geothermal system. The main results unravel the presence of deep regional pathways along which endogenous fluids circulate before being discharged in the investigated areas. The peripheral zone emissions are affected by interaction with shallow aquifers and condensation processes whereas the CO2 emitted from the central areas, located near the core of the geothermal system, was accompanied by high amounts of steam, and suffers intense shallow fractionation processes. The latter areas emit medium‐to‐low normalized‐CO2‐degassing rates (<270 t d−1 km−2) when compared to the extremely high values occurring in the peripheral sectors (up to 1,300 t d−1 km−2) of the Larderello geothermal systems, possibly suggesting an incipient propagation of such a system, likely wider than previously thought. Plain Language Summary High‐temperature geothermal areas are specific zones on Earth where the geothermal gradient is greater than the average global value (∼30°C km−1). This is due to the existence of cooling magma source(s) at depth, providing heat that is transmitted to fluid reservoir(s) located at intermediate levels continuously and naturally fed by recharging fluids, and sealing rock(s) at shallower levels that maintain reservoir temperature and pressure. These geothermal areas commonly show steam‐dominated manifestations at the surface, accompanied by relevant degassing of carbon dioxide likely originated from different feeding systems (biogenic, thermometamorphic, and mantellic). Defining sources, processes, and transport mechanisms governing the CO2 emissions from soils is challenging but pivotal to understand the geothermal fluid origin, dynamics, and relation with the geological structures. To unravel these processes, we combined geochemical and structural measurements performed at the Larderello‐Travale‐Radicondoli (LTR) geothermal field (Italy). Distinct geothermal sectors were investigated according to their geochemical characteristics, CO2 degassing rates, and geological‐structural features, to understand how CO2 is transported and modified during its journey from the deep geothermal reservoir(s) to the surface, exploiting the permeability of fault zones and/or fractured rocks. Results suggest that the LTR geothermal system might be wider than previously thought, indicating a higher geothermal potential. Key Points Extensive CO2 soil degassing measurements and carbon isotopic composition in the Larderello geothermal system were carried out Hydrothermalized hot‐ and cold‐degassing areas are controlled by structural setting Regional transfer zones enhance the circulation of deep‐seated geothermal fluids

The thermal evolution of the crust during continental collision evolves from cold to hot with time, which impacts crustal reworking and differentiation. However, it remains elusive as to the mechanism driving the crust to be hot during the protracted collision. Here, we describe crust thermal evolution via detailed petrographic and geochronological analyses, and P−T calculations on different metamorphic rocks from east‐central Himalaya, which record a wide range of P−T conditions and ages from the early to the late collision stage. The Eocene (ca. 44 Ma) metamorphism, represented by the Kangmar garnet amphibolite, exhibits P = ∼12 kbar, T = 670°−690°C, and a geothermal gradient of 17.0°–17.4°C/km. Rocks in the Tsona area yield metamorphic ages of 39–36 Ma and peak P−T conditions of 13.0–14.5 kbar and 760°−770°C (16.0°−17.9°C/km). Mafic granulites recorded variable peak conditions of 18–25 kbar and 720°−870°C (8.72°−14.6°C/km) and were overprinted by granulite‐facies metamorphism of ∼8 kbar, 916°−932°C (∼33.3°C/km) at ∼15 Ma. These results indicate that the Himalayas exhibited elevated thermal gradients during protracted collisions. Given the thick felsic crust and high rate of heat production, thermal modeling results indicate that radiogenic heating during prolonged collision caused the Himalayan crust to be hot, even to ultra‐high temperature conditions, and led to the elevated geothermal gradients. As a premier example of continental orogenesis, the Himalaya is distinctly hotter than the cold Alpine‐type orogens. This thermal difference could stem from a reduced convergence rate, low‐angle underthrusting, vigorous felsic magmatism, and persistent shear heating.

The present geothermal characteristics and influencing factors are analyzed to conduct geothermal resource exploration in the Xiong’an New Area. Thermal conductivity data for 100 rock samples are obtained from different wells and a sedimentary strata thermal conductivity column is proposed. From these data, heat flow distribution in the area is mapped using equilibrium temperature logs obtained for 32 wells. The heat flow in this area is found to be 53.3–106.5 mW·m−2 (average: 73 mW·m−2). The uplift heat value in Niutuozhen and Rongcheng uplift is 106.5 and 90 mW·m−2, respectively. The sag heat flow is relatively low and the Baxian sag’s heat flow value is 48.9–61.6 mW·m−2. Thermal conductivity differences among Cenozoic caprock, Proterozoic carbonate reservoirs, and basement rock mainly affects the geothermal distribution. The low and high thermal conductivities of the caprock and thermal reservoir as well as basement, respectively, cause heat flow redistribution in the surface during conduction. Groundwater rises to geothermal reservoirs through heat-controlling faults, causing convective heat transfer and increasing the geothermal reservoir temperature; therefore, high-temperature groundwater accumulates in the shallow uplift areas. The caprock’s thin uplift area exhibits a high geothermal background due to water convergence. Understanding the geothermal characteristics and influencing factors is necessary for understanding the distribution law and factors influencing geothermal resources and guiding geothermal exploration and development in the Xiong’an New Area.

Environmental degradation is reducing crop productivity in many regions of Egypt. Moreover, unsustainable surface water drainage contributes to salinized soil conditions, which negatively impact crops. Egypt is seeking solutions to mitigate the problem of surface water drawdown and its consequences by exploring renewable and sustainable sources of energy. Geothermal energy and the desalination of saline water represent the only solutions to overcoming the fresh water shortage in agricultural industry and to providing sustainable fresh water and electricity to villages and the Bedouin livelihood. In Egypt, the Siwa Oasis contains a cluster of thermal springs, making the area an ideal location for geothermal exploration. Some of these thermal springs are characterized by high surface temperatures reaching 20 °C to 40 °C, and the bottom-hole temperatures (BHT) range from 21 °C to 121.7 °C. Pre-Cambrian basement rocks are usually more than 440 m deep, ranging from 440 m to 4724.4 m deep. It is this feature that makes the Siwa Oasis locality sufficient for geothermal power production and industrial processes. This study utilized both the Horner and the Gulf of Mexico correction methods to determine the formation temperatures from BHT data acquired from 27 deep oil wells. The present study revealed a geothermal gradient ranging from 18 to 42 °C/km, a heat flux of 24.7–111.3 mW/m2, and a thermal conductivity of 1.3–2.65 W/m/k. The derived geothermal, geophysical, and geological layers were combined together with space data and the topographic layer to map relevant physiographic variables including land surface elevation, depth to basement, lineament density, land surface temperature, and geologic rock units. The ten produced variables were integrated in GIS to model the geothermal potential map (GTP) for the Siwa Oasis region. According to the model, both the eastern side and north and northeastern portions of the study region contain high and very high geothermal potential energy. Combining bottom-hole temperature measurements with satellite remote sensing and geospatial analysis can considerably enhance geothermal prospecting in Egypt and other East African areas that have geologically and tectonically similar settings. In addition to identifying sustainable resources needed for food production, this research has implications for renewable energy resources as well.