Regularity Analysis of Airborne Natural Gamma Ray Data Measured in the Hoggar Area (Algeria) - Advances in Data, Methods, Models and Their Applications in Geoscience - page 94

The local Hölder exponent (or local regularity) maps obtained from the GR data recorded in
the K, Th and U channels, using a multiple filter technique that we generalize to a 2D-case,
exhibit almost an identical image. Besides, they allow to locate the faults affecting the
studied zone.
2. Regional geology
The Hoggar is a large shield area covering approximately 550,000 km 2 . It includes an
important surface of the Tergui shield, prolonged in South-east, in Mali, by the solid mass of
Iforas and in the East, in Niger, by the solid mass of Aïr (Fig. 1).
The Hoggar belongs to the Trans-Saharan pan-African chain (Cahen et al. , 1984, Liégeois et
al ., 1994). It is crossed by two major submeridian faults, located at longitudes 4°50' and 8°30',
which delimit three longitudinal compartments (Eastern, Central and Western), with
different structural and lithological characteristics. This geological configuration resulted by
an extreme E-W compression, during the pan-African (600 My), of the Touareg shield by
two rigid plates: the Western African craton and the Eastern African craton (Bertrand and
Caby, 1978; Black et al. , 1979).
Western Hoggar
Central Hoggar
Eastern Hoggar
1 - Archaean granulites; 2 - Gneiss and metasediments, series of Arechchoum (Pr1); 3 - Gneiss with
facies amphibole, series of Aleskod (Pr2); 4 - Indif. gneiss (Pr3); 5 - Pharusian Greywackes; 6 - Arkoses
and conglomerates, series of Tiririne (Pr4); 7 - Volcano-sediments of Tafassasset (Pr4); 8 - Molasses
(purple series) of Cambrian; 9 - Pan-African syn-orogenic granites; 10 - Pan-African Granites; 11 - Pan-
African post-orogenic granites; 12 - Granites of Eastern Hoggar; 13 - Late pan-African Granites;
14 - Basalts and recent volcanism; 15 - Paleozoic cover; 16 - Fault.
Fig. 1. A simplified geological map of the Hoggar (Caby et al. , 1981, modified)