Download NUMERICAL MODELING OF GEOTHERMAL FIELDS IN BLACK SEA

NUMERICAL MODELING OF GEOTHERMAL FIELDS IN BLACK SEA
AND ITS GEOLOGICAL INTERPERTATION
Simeon Kostyanev1, Georgi Trapov1, Atanas Vasilev2, Velislav Stoyanov1
1
University of Mining & Geology, Sofia, BG; 2Institute of Oceanology, BAS, Varna, BG.
([email protected]; [email protected]; [email protected]; [email protected])
Keywords: Numerical Modeling, Black Sea, Temperature, Heat Flow, Heat Production
Numerical modeling of geothermal fields in Black Sea is of great significance when creating
integrated geophysical models of the region and their geological interpreting. Temperature calculation
requires the solution of the heat conductivity equation with corresponding boundary conditions. This
means extrapolating the measured on the sea bottom heat flow in accordance with assumptions
concerning the deep structure of the main geological provinces (based on the explosion seismology), the
depth distribution of the heat sources, and the thermal conductivity coefficient. Up to now in Black Sea
are measured about 700 value of heat flow [1], part of which we used in our models.
In this paper a numerical solution of the steadystate heat conductivity equation in an inhomogeneous
media was used to calculate temperature distribution in
earth’s crust and upper mantle in Black Sea along three
profiles (Fig.1): div(KgradT) = -A, where K(x,y,z,T) is
temperature dependent thermal conductivity; A(x,y,z)
heat production; T(x,y,z) temperature and x,y,z are
coordinates. The boundary conditions are: 1)
T(x,y,z=0)=To(x,y) - sea bottom temperature; 2)
 T/  x=  T/  y=0 - symmetry of the temperature
fields at the vertical boundary; 3) The last boundary
condition – the knowledge of temperature or
heat flow at the base of the model, is problematic and
Fig.1. Scheme of heat flow stations in Black
as rule this information is not available. The solution of
Sea Basin with profiles I, II, III.
the above problem requires the solution of the inverse
problem [2, 3]. To define the block crustal structure and the corresponding distribution of heat sources,
the results of deep seismic sounding and new seismological tomography were employed. The crosssection along profiles I, II and III presents a 6-layers media [4]. The proper calculation of the temperature
field was performed by the program package Solid Works (COSMOS) 2011. The results of temperature
modeling are summarized in schemes, which show the calculated temperatures related to 10, 30, 50, and
70 km. The agreement of calculated temperatures at the points of intersection of the investigated profiles
is generally good. The corrected bottom sea heat flow due to the effect of sedimentation range from 50 to
70 mW/m2 [1]. The regional variation of the Moho temperature is from 380 to 720oC. The Moho heat
flow may range from 15-25 to 30-40 mW/m2. The crustal contribution to the bottom sea heat flow due to
radiogenic heat sources amounts to 10-25 mW/m2 The results clearly confirm the possible existence of
the astenosphere under the Black Sea basin. Temperature modeling permits assessing the thickness of the
thermal lithosphere. An attempt for a new geological interpretation was performed.
References
[1] Kutas, R., V. Kobolev and V. Tsvyashchenko. Heat Flow and Geothermal Model of the Black Sea
Depression: Tectonophysics, v. 291, 91-100, 1998.
[2] Kostyanev S. Mathematical Modeling of Geophysical Fields in Gradient Media (Monograph), Sofia,
200 p.,1999.
[3] Vassilev A., V. Tsvyashchenko. Thermal Field of the Earth's Crust of the Bulgarian Black Sea
Continental Slope - Inverse Problem Theory Interpretation. In: Geological Evolution of the Western
Part of the Black Sea Basin in Neogene-Quaternary, BAS, Sofia, 622-630, 1990.
[4] Gobarenko V., T. Egorova. Structure of Lithosphere and Geodynamics in Black Sea Basin, Moscow,
Journal Physics of Earth, 6, 50-66, 2010