Mapeamento da isoterma de Curie na Bacia do Parnaíba estimada através da profundidade da base das fontes magnéticas
Located on the western edge of the Brazilian northeast, the Parnaiba Basin is an
intra cratonic basin with oil production. This study aims at understanding its genesis
and evolution, using aeromagnetic and gravity data. We used the spectral analysis of
aeromagnetic data to map the depth to the bottom of the magnetic sources in order to
assimilate this depth with the depth of the Curie isotherm, and infer the geothermal
gradient.
Using the spectral analysis technique, we succeeded in mapping the surface of
the depth to the bottom of magnetic sources (SBFM), which marks the depth that
occur magnetization. In the Parnaiba Basin the SBFM presented depths around -20,5
and -28,5 , which was consistent with an inversion of the same dataset using the
technique of Magnetization Vector Inversion (MVI). Furthermore, SBFM topography
correlates well with Moho depth, which was estimated from satellite gravimetric data
from the GOCE mission (Gravity Field and Steady-State Ocean Circulation Explorer).
Assuming that SBFM coincides with the Curie isotherm of magnetite (ICM),
defined as the surface at which magnetite ( ) looses its ferromagnetic properties,
it was possible to estimate the geothermal gradient. The geothermal gradient in the
basin showed values between 19.2 and 26.5 , allowing to estimate the heat flow
for the Parnaiba basin after assuming a conductivity of 2.69

. The resulting
heat flow values ranged between 51.6 and 71.3
, which is consistent with
values found in other works throughout the South American continent. Lithospheric
thickness using an empirical relationship, finding values between -65.8 and -89.2 .
We propose that thermal structure of Parnaiba basin is influenced by a deep
thermal anomaly. This anomaly has heated the lithosphere beneath the basin and has
resulted in relatively thin values for the lithospheric thickness and relatively high
surface heat flow values. The origin of the anomaly is not clear, but the correlation
between Curie depth and Moho topography, suggests that tectonic extension processes
could have played a role.