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Terrestrial Heat Flow in Geothermal Energy in Asia
... The heat flow generally varies from 53 to 130 mWm-2 and shows the expected inverse relationship with the CPD. Yamano (1995) observed that shallow CPDs are in agreement with elevated heat flow. Elevated heat flow exists in Ikeja, Ikorodu and Igbonla areas in the central and northwestern regions respectively, while the western region is essentially characterised by low heat flow. ...
Geothermal resource has attracted industrial and environmental interest in the last decades. However, the thermal condition of the Dahomey basin, which is instrumental to harnessing such geothermal resource, has remained largely unknown. The geothermal characterisation of Dahomey Basin was therefore undertaken to determine its thermal potential. The methodology involved analysis of the power spectra density of aeromagnetic data and interpretation of geo-resistivity data. The aeromagnetic dataset was divided into twenty one blocks with each block overlapping the adjacent blocks by 50%. Spectra peak, Curie depth, geothermal gradient, heat flow and temperature at depth were computed. Two-dimensional geo-resistivity profiling method was implemented to locate the top of the thermal aquifer. The results showed varied Curie depth (11–27 km) and heat flow (53–130 mW/m²) while the geothermal gradient ranges from 21 to 52 °C/km. Results of resistivity profiling showed the thermal aquifer to be sand (1–20 Ωm) whose top is located at 155 − 210 m depth. From the estimated geothermal parameters, two new geothermal prospect areas were identified. This study established that Dahomey basin is a thermally unstable basin with a very high potential for geothermal resource that is attributable to crustal thinning and possibly mantle dynamics.
... We derived heat flow values in the range of 49-64 mW/m 2 (Fig. 12b). The average heat flow in the study area is approximately 56 mWm −2 , which is considered typical of continental crust [52]. The heat flow values show a general increasing trend towards the southern and northern margins of the Siwa Oasis. ...
Siwa Oasis is a part of the greatest northern depression in the Egyptian Western Desert, located just 50km east of the Libyan border. It represents one of the most interesting potential candidates for the development of the Northern Western Desert of Egypt. Temperature data from deep wells in the Western Desert of Egypt indicate low geothermal resources. Here, we present the contribution of airborne gravity and magnetic geophysical data for the preliminary exploration of geothermal potential in Siwa Oasis. To achieve this objective, a 3D inversion of aerogravity data was used to delineate the depths to basement rocks, while spectral analysis of the aeromagnetic data was used to estimate the Curie Point Depth (CPD) and provide geothermal gradient and heat flow maps for the Siwa Oasis. The depth to the Precambrian basement rock is commonly greater than 2km, ranging from 2km to 5km, whereas the CPDs range from 21km to 28km. Our results imply an inverse relationship between these two depths, in which the deeper basement regions are associated with shallow Curie depths. The derived geothermal gradients range from 21 to 27°C/km and the heat-flow values range from 49 to 64mW/m² for the study area.
... Heat flow investigators also came out with similar findings. Gupta et al. (1991) and Gupta (1994), based on analysis of available heat flow data, indicated presence of a more than 200 km thick lithosphere beneath Archean Dharwar craton and Deccan volcanic provinces. They also analysed heat flow data from various Precambrian terrains of the world (Gupta, 1993) and expressed that the Indian shield is neither hotter than other Gondwana shield, nor its super mobility affected its thermal characteristics. ...
The nature of crustal and lithospheric mantle evolution of the Archean shields as well as their subsequent deformation due to recent plate motions and sustained intraplate geodynamic activity, has been a subject of considerable interest. In view of this, about three decades ago, a new idea was put forward suggesting that out of all shield terrains, the Indian shield has an extremely thin lithosphere (∼100 km, compared to 250–350 km elsewhere), apart from being warm, non-rigid, sheared and deformed. As expected, it met with skepticism by heat flow and the emerging seismic tomographic study groups, who on the contrary suggested that the Indian shield has a cool crust, besides a coherent and thick lithosphere (as much as 300–400 km) like any other shield. However, recently obtained integrated geological and geophysical findings from deep scientific drillings in 1993 Killari (Mw: 6.3) and 1967 Koyna (Mw: 6.3) earthquake zones, as well as newely acquired geophysical data over other parts of Indian shield terrain, have provided a totally new insight to this debate. Beneath Killari, the basement was found consisting of high density, high velocity mid crustal amphibolite to granulite facies rocks due to exhumation of the deeper crustal layers and sustained granitic upper crustal erosion. Similar type of basement appears to be present in Koyna region too, which is characterized by considerably high upper crustal temperatures. Since, such type of crust is depleted in radiogenic elements, it resulted into lowering of heat flow at the surface, increase in heat flow contribution from the mantle, and upwarping of the lithosphere-asthenosphere boundary. Consequently, the Indian shield lithosphere has become unusually thin and warm. This study highlightes the need of an integrated geological, geochemical and geophysical approach in order to accurately determine deep crust-mantle thermal regime in continental areas.
... This is justified because in these regions, the subducting Pacific plate has the similar age (ca. 130 Ma, Nakanishi et al., 1992) and dip angle, and the observed heat flows in the forearc are also similar (Yamano, 1995). The isotherms in the stability field of the fore-arc wedge show a curved structure with a higher temperature at the inside of the corner. ...
The seismicity in the subducting Philippine Sea slab (PHS) beneath southwest Japan shows a variety of modes of occurrence. We try to explain this variety on the basis of dehydration embrittlement in the subducting oceanic crust and/or mantle. The PHS subducting along the Nankai Trough shows commonly a single narrow seismic zone shallower than 60 km, which may reflect dehydration embrittlement in the hydrated subducting oceanic crust only, implying the lack of hydrated slab mantle. The PHS beneath Kanto, however, shows a double seismic zone (Hori, 1997) in the mantle part. Here the serpentinized mantle wedge of the Izu-Bonin fore-arc is subducting, and the double zone can be explained by its dehydration. Beneath Kii Peninsula and Kyushu, seismic events within the slab mantle have also been detected. This indicates that the PHS mantle beneath these areas is also hydrated, which may have resulted from subduction of the serpentine stable in the Izu-Bonin back-arc area. Aqueous fluids released from the serpentinized mantle beneath Kii Peninsula may have initiated partial melting in the mantle wedge, as indicated by the presence of high 3He/4He ratios in the natural gasses and the shallow seismic swarms in this region (Wakita et al., 1987). Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences.
Geothermal waters are valuable natural resources for direct uses, societal beneits, and industrial uses. Geochemical classii-cation of physicochemical parameters of seven geothermal sources at Gujarat was evaluated in order to improve and identify their possible applications. The analysis of geothermal spring water was performed using standard methods. Metal elements were determined by atomic absorption spectroscopy (AAS). The waters were categorized as Na + K and Cl + SO 4 based on results obtained from Piper, Durov, and Stif analysis. The Tuwa, Dholera, and Lasundra thermal waters had relatively high salinity values exceeding 5000 mg/l. This study gave an insight into the origin of water which could be due to the interaction of underground water with granitic basement/plutons. Due to high total dissolved solvent (TDS) values in places like Dholera, Tuwa, and Lasundra, the water cannot be used for daily life purposes like bathing, drinking, irrigation, etc. while in places like Tulsishyam, Savarkundala, Unai and Lalpur the TDS content was such that it can be used for daily uses.
The nature of crustal and lithospheric mantle deformation due to sustained intraplate geodynamic activity beneath a unique Archean shield terrain like India, has been a subject of considerable interest. So far, heat flow is evaluated for over 170 locations over this terrain, which regionally varies from a low of 23.0 mW/m² to as high as 107.0 mW/m². Their distribution conforms well with the nature of underlying crust and mantle inhomogeneities. Among various cratons, the Archaean Dharwar craton is characterised by lower heat flow, compared to remobilised Sighbhum, Bastar and Aravalli cratons. Similarly, lithospheric thickness also varied from as low as 45 km in north Cambay graben to 185 km below western Dharwar craton, with a mean of about 100 km. These findings re-affirm that the Indian crust, as well as mantle, is quite warm due to rise of isotherms at shallow level. Thinning of the Indian lithosphere may be due to the combination of both, Deccan volcanic event and continued lithospheric remobilization since Midproterozoic period.
The super dynamic Indian peninsular shield remained quite active during its entire course of geologic history, compared to all other similar terrains in the world. It is associated with distinct geologic, geotectonic and magmatic signatures. Indian shield underwent large scale deformation and degeneration at crust and lithospheric mantle level, due to sustained thermo-geodynamic perturbations, specially during the Cretaceous period, when the Earth was passing through an extremely dynamic phase. Its original texture and composition is no more the same, as revealed by deep scientific drillings carried out in Deccan volcanic terrain, which is considered one of the largest flood basaltic provinces on the surface of the Earth. Historically, it has been associated with a moderate intraplate seismic activity, usually not found in stable continental regions. Such unusual characters are very well reflected in all the geophysical fields.
Intraplate seismicity in the Indian shield is confined to the upper 10-15 km except for the Jabalpur and Satpura events which occurred at a depth of 35-40 km in the region bounded by the Narmada-Son and Tapti lineaments, two major palaeo-rift-related tectonic features in the central Indian shield. Interestingly, high surface heat flow of 70-100 mW/m2 has been suggested for the above region. Rheological models of continental crust in such a high heat flow regime do not support occurrence of deep crustal seismicity. In the present work we computed a range of Theological models for the region for different values of thermal parameters and analysed these in light of deep crustal seismicity. The study suggests that mantle-derived heat flow should be significantly low for the occurrence of deep crustal events in the above region and the excess surface heat flow could be a manifestation of fluid advection in the uppermost part of the crust, as is evident from the presence of many hot springs.
The position of lithospheric magnetic anomalies, detected in total magnetic intensity and the vertical component of the magnetic field, has been determined for Siberia using data from the CHAMP satellite. The paper describes the technique for the satellite data processing and the ways of recognition of regional lithospheric magnetic anomalies from satellite-measured values of the total geomagnetic field, which are obtained from several sources (external and internal with respect to the Earth’s surface). Maps of magnetic-field anomalies of different scales have been constructed for several regions of Siberia depending on the method of areal averaging. The possible geologic and physical nature of the magnetic anomalies and their relationship with deep-seated crustal structures are considered. Preliminary interpretation of the magnetic-field maps shows that the anomalies are connected with the present-day large geologic and geophysical elements of the basement. The features of the lithospheric magnetic field, as a parameter reflecting the present position of tectonic structures and their physical properties, can be used for their contouring in combination with other geological and geophysical methods.
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