Airborne data processing and 3D modeling of magnetic structures between Nador region and the Chaffarine Islands: Geological significances

Abstract

The Cap of Trois Fourches-Nador-Chaffarine Islands zone (CTF-N-CI) located in the Moroccan Oriental Rif is recognized by Neogene-Quaternary volcanic outcrops. Those later formed volcanic cones and are considered the main source of the huge Nador magnetic anomaly. This study aims to enhance the magnetic context using geophysical techniques and identify the geometry of magnetic sources by performing 3D modeling using Talwani method. We have achieved the following findings: (1) The elaborated residual magnetic map (Rs) that shows three aligned magnetic anomalies. They are oriented W-E and register a maximum intensity of 380 nT. Applying reduction to the pole to (RTP) the Rs map makes the anomalies on the top of their body sources. Thus, we have found that those anomalies have resulted essentially from the Gourougou volcano and Chaffarine Islands volcanoes outcropping in the study area. Except for the middle Pm anomaly, which is related to volcanic rocks of the Kariate Arekmane drillhole. (2) Performing horizontal derivative (HD) technique leads to establishing the edges of the source bodies. Hence, the inversed map of the magnetization distribution proves that the three bodies are homogeneous and probably splintered from a unique mass. (3) The downward up continuation (DC) to different heights (from 500 to 2000 m) indicates the source's depth. Thus, we have demonstrated that the common source could reach 0.6 km of altitude. (4) Finally, we have constructed a 3D Talwani model of the volcanic edifices. The released 3D model demonstrates that the anomalies are related to a very extensive mass of 80 km in length, 20 km in width, 1.3 km in thickness. This model supports that the Neogene-Quaternary volcanism of the study area was fissural and related to the W-E fracture zone of up to 80 km in length. This volcanism was also affected by the sinistral Nekor fault, which probably made the Trois Fourches Cap body isolated from the other volcanic edifices.Previously mentioned elements probably prove the simultaneous establishment of this large magnetic structure. Moreover, they emphasize the crucial role of the magmatic phenomena which occurred in Northeastern Morocco at the beginning of the Messinian.