New global maps of the depth to the boundary between the lithosphere and the asthenosphere are presented. The maps are based on updated global databases for heat flow and crustal structure. For continental regions the estimates of lithospheric thickness are based on determinations of subcrustal heat flow, after corrections for contributions of radiogenic heat in crustal layers. For oceanic regions the estimates of lithospheric thickness are based on the newly proposed finite half-space (FHS) model. Unlike the half-space cooling (HSC) and the plate models the FHS model takes into account effects of buffered solidification at the lower boundary of the lithosphere and assumes that the vertical domain for downward growth of the boundary layer have an asymptotic limit. Results of numerical simulations reveal that theoretical values derived from the FHS model provide vastly improved fits to observational data for heat flow and bathymetry than can be achieved with HSC and plate models. Also, the data fits are valid for the entire age range of the oceanic lithosphere. Hence estimates of depths to lithosphere- asthenosphere boundary (LAB) based on the FHS model are believed to provide more reliable estimates than those reported in previous thermal models. <br><br> The global maps of depths to LAB derived in the present work reveal several features in regional variations of lithosphere thicknesses that have not been identified in earlier studies. For example, regions of ocean floor with ages less than 55 Ma are characterized by relatively rapid thickening of the lithosphere. Also there is better resolution in mapping the transition from oceanic to continental lithosphere, as most of the latter ones are characterized by lithospheric thickness greater than 150 km. As expected the plate spreading centers in oceanic regions as well as areas of recent magmatic activity in continental regions are characterized by relatively thin lithosphere, with LAB depths of less than 50 km. On the other hand, the areas of continental collisions and Precambrian cratonic blocks are found to have lithosphere thicknesses in excess of 250 km. Regional variations of lithosphere thickness in the interiors of continents are found to depend on the magnitude of subcrustal heat flux as well as the tectonic age of crustal blocks

The present work provides a new look into the nature and distribution of geothermal resources of South America, on the basis of recent advances in data analysis and regional assessments. Notable in this context is the progress achieved in the use of a procedure termed as magmatic heat budget (MHB) that allow estimation of heat flux in areas of recent volcanic activity. In addition, an updated compilation of temperature gradients and heat flux have been completed. Such advances have allowed new resource assessments for 6526 sites. These span over more than 100 crustal blocks, distributed in thirteen countries of the continent. Following this, a 2ox2ogrid system with homogenized data sets were employed for calculating the in-situ heat content. Determinations of resource base based on observational data are now available for 253 out of a total of 418 cells in this grid system. Values of resource base based on estimated heat flow were calculated for the remaining 165 grid elements. The data and model results on temperatures of subsurface strata at depths less than three kilometers have been employed in classifying the resources, into three general categories: hot dry rock (HDR), hot wet rock (HWR) and low enthalpy (LE). HDR type resources, classified as those with temperatures higher than 150oC, occur in 318 localities mainly in the Andean regions. Similarly, HWR type resources, classified as those with temperatures in the range of 90 to 150oC, occur in 352 localities. Low enthalpy (LE) resources, with temperatures < 90oC, are numerous mainly in the eastern parts of the continent. The total resource base (RB) of HDR systems is estimated to be 1329x1021J and the corresponding resource base per unit area (RBUA) is 513GJ/m2. The HWR systems have a total resource base of 586x1021J, while the corresponding value for RBUA is 409GJ/m2. The low enthalpy systems, with temperatures in the range of 60 to 90oC, have a total resource base of 240GJ/m2, while those with temperatures less than 60oCis estimated to be 210GJ/m2. There are indications that HDR resources, with temperatures higher than 150oC at depths less than three kilometers, occur in 318 localities of the Andean regions. The total resource base (RB) of HDR systems is estimated to be 1329x1021J, while the corresponding weighted mean resource base per unit area (RBUA) is estimated to be 513GJ/m2. The new results have also been useful in regional scale identification of resources with notable pore fluid circulation, classified as HWR systems. Such systems with temperatures in the range of 90 to 150oC, are inferred to occur at depths less than three kilometers, in 352 localities of the Andean region. The total resource base of HWR systems is estimated to be 586x1021J, while the corresponding value for RBUA is estimated to be 409GJ/m2. Low enthalpy (LE) resources, with temperatures in the range of < 90oC, are numerous in the remaining parts of Andean regions and also in the eastern parts of the continent. The resource base per unit area of low enthalpy systems with temperatures in the range of 60 to 90oC is estimated to be 240GJ/m2, while that for systems with temperatures less than 60oCis estimated to be 210GJ/m2.

New global maps of the depth to the boundary between the lithosphere and the asthenosphere are presented. The maps are based on updated global databases for heat flow and crustal structure. For continental regions the estimates of lithospheric thickness are based on determinations of subcrustal heat flow, after corrections for contributions of radiogenic heat in crustal layers. For oceanic regions the estimates of lithospheric thickness are based on the newly proposed finite half-space (FHS) model. Unlike the half-space cooling (HSC) and the Plate models the FHS model takes into account effects of buffered solidification at the lower boundary of the lithosphere and assumes that vertical domain for downward growth of boundary layer have an asymptotic limit. Results of numerical simulations reveal that theoretical values derived from FHS model provide vastly improved fits to observational data for heat flow and bathymetry than can be achieved with HSC and Plate models. Also, the data fits are valid for the entire age range of the oceanic lithosphere. Hence estimates of depths to lithosphere – asthenosphere boundary (LAB) based on FHS model, are believed to provide more reliable estimates than those reported in previous thermal models. The global maps of depths to LAB derived in the present work reveal several features in regional variations of lithosphere thicknesses that have not been identified in earlier studies. For example, regions of ocean floor with ages less than 55 Ma are characterized by relatively rapid thickening of the lithosphere. Also there is better resolution in mapping the transition from oceanic to continental lithosphere, as most of the latter ones are characterized by lithospheric thickness greater than 150 km. As expected the plate spreading centers in oceanic regions as well as areas of recent magmatic activity in continental regions are characterized by relatively thin lithosphere, with LAB depths of less than 50 km. On the other hand, the areas of continental collisions and Precambrian cratonic blocks and are found to have lithosphere thicknesses in excess of 250 km. Regional variations of lithosphere thickness in the interiors of continents are found to depend on the magnitude of subcrustal heat flux as well as the tectonic age of crustal blocks

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Updated data for 1417 localities have been assembled for purposes of assessments of geothermal resources in South America. Analyses of these data sets have allowed improved estimates of geothermal resource base and recoverable resources for thirteen countries in the continent. The results obtained have also allowed identification of more than 20 crustal blocks where the resource base per unit area (referred to the accessible depth limit of 3 km) is in the range of 100 to 1000 Giga Joules, while the recoverable resources per unit area are in the range of 1 to 100 Giga Joules. Most of the high temperature resources occur within regions of recent tectonic activities in southern and central Chile, highlands regions in Bolivia, and several localities along the magmatic arc covering western Ecuador, central volcanic belt of Colombia and northern Venezuela. In addition, isolated pockets of geothermal resources have been identified along the eastern Andean belt of Peru. There are indications of occurrence of medium and low temperature geothermal resources at depths of 1 to 3 km in several regions in the eastern sectors of the continent, mainly in the northeastern and central parts of Brazil. In addition, considerable progress has been made in assessments of low temperature resources associated with deep fracture systems in Precambrian terrains. Progress has also been achieved in assessment of low temperature resources in deep aquifers of Paleozoic sedimentary basins. The results of such estimates are currently being considered for planning large-scale exploitation of the Guarani aquifer system, which spans over large areas of western Uruguay, northern Argentina and southern Brazil.

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