Geothermal Anomalies and Analysis of Gravity, Fracturing and Magnetic Features in Morocco

Abstract

Heat flow determinations in Morocco show two main geothermal anomalies: -Northward, we observe from the northern Middle Atlas, the Rif and North-eastern Morocco toward the Alboran Sea, South-east Spain and Western Algeria a range of 80 - 110 mW/m? and 35-50 ?C/km for heat flow density and thermal gradient respectively. Southward, an East-West geothermal trend is observed from the Canary archipelagos to Tindouf basin and which continues in the Algerian Sahara (with a wide geothermal field range of 70-100 mW/m? and 25-45 ?C/km for heat flow and geothermal gradient respectively). The isopleths map reveals significant short-wavelength anomalies overprinting these regional variations, particularly, in the Rif and the High Atlas, where negative residual heat flow anomalies are superimposed on low Bouguer anomalies (reaching -150 mgal in both domains), and are probably associated to thick deposits.
These two regional geothermal anomalies could be the result of the same phenomenon of an abnormally hot and heterogeneous upper mantle, in relation to an extensional tectonic regime over Northwest Africa and the Betic-Rif orocline, since the Cretaceous rifting and the Alpine orogenesis.
The highest geothermal anomaly observed in the north-eastern part of the country (Middle Atlas and Eastern Rif), is particularly characterized by intensive Quaternary volcanism and an average shallow Curie points depths of 15 to 20 km. On the other hand, the spatial distribution of the hot springs presenting CO2 emission extends preferentially along a NE-SW seismic lineament corresponding to the zone of High and Middle Atlas. Also we note the existence of areas showing shallow Curie points depths (15 to 20 km) in the Atlas domain. These phenomena are consistent with the thermal litospheric structure underneath the Atlas belt, where a modelling by using thermal, seismic, topographic and gravity data reveals an unusually thin lithosphere (less than 90 Km).