Abstract
Four heat flow density values and five temperature-depth profiles were obtained in a heterogeneous region considering heat flow by conduction in the vertical direction, and heat sources in the crust due to radioactivity decay. The heat produced in the upper layers of the crust was obtained based on gamma-ray charts and published data of laboratory radioactivity measurements on samples taken from the region. Seismic data were used to obtain the thickness of the different layers of the upper and middle crust and the depth of the Moho discontinuity considered coincident with the crust/mantle boundary. The heat flow at the surface is obtained by adding the heat flow from the mantle with the heat generated by the radioactive sources in the crust. The method was applied to a region with one measured heat flow density value (Ourense) and four points without any heat flow density measurement. A heat flow value from the mantle was obtained with Ourense data. Special attention was given to a region (A) with a seismic anomaly near the surface. The anomaly was explained by mass deficit near the surface that gives rise to an abnormal density value and an increase in seismic wave velocity values. The decrease in density is due to the presence of water in the region forming an aquifer. Geothermometer values obtained from samples of water in the thermal springs of Tuy (Spain) and Monção (Portugal) were used as the water temperature at the bottom of the aquifer. Isostatic balance in the region was considered to obtain density values and the amount of water in the region. Thermal conductivity and radioactivity heat source values in the region were obtained considering the amount of water in the region. Values from 86 to 97 mW/m2 were obtained using the same value of heat flow from the mantle. This is due to different values of heat produced in the crust due to different thickness layer values or/and to different heat production values.
Highlights
The principal aim of this work is to obtain information about heat flow density and temperature-depth values in a region without measured heat flow density values using different types of geophysical data obtained in the region for other purposes and available from the literature
The differences in heat flow values at the surface are mainly due to heat sources in the crust and thickness of their layers
A velocity seismic anomaly “yellow zone” and the heat flow density value obtained in this zone may be explained by a low-density value and lower heat production and thermal conductivity in crustal layers with water in the region
Summary
The principal aim of this work is to obtain information about heat flow density and temperature-depth values in a region without measured heat flow density values using different types of geophysical data obtained in the region for other purposes and available from the literature. The main type of geological formations in the region is granitic rocks traversed by several faults and two hot springs are identified near latitude 42.2 (Model-A). Three different ages of granites with different contents of Uranium Thorium and Potassium were identified in the region in formations with different thicknesses. These results are complemented by radiometric charts presenting high values of exposure rates in the region. The heterogeneity of the region is shown on seismic models of the crust (vertical profiles and horizontal distributions at several depths) and in gravity data. Geoid height values over 56.0 m were obtained in the region except in model E where a value of 55.85 m was found
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
