AN INVESTIGATION OF THE EXTERNAL PRE-RIF OF NORTHERN MOROCCO USING GRAVITY AND SEISMIC REFLECTION DATA

The Rif, Betics, and Tell Atlas comprise an arcuate mountain chain that encircles the Alboran Sea and encompasses the westernmost belt of the Alpine Orogeny. The Atlas Mountains of northeastern Morocco consist of the High Atlas and Middle Atlas. Both of these mountain belts underwent deformation that began during the late Mesozoic with the opening of the Atlantic and the western Neo-Tethys Oceans and continued throughout the Cenozoic with the collision between Africa and Europe. The two mountain belts, however, are fundamentally different. Post-convergent extension of Pangaea recorded in synrift basins began in the Late Triassic and continued into the Early Jurassic. This resulted in widespread extensive episodes resulting in the reactivation of Hercynian thrusts. The Atlas system underwent northwest-southeast extension during this time relative to the opening of the Atlantic Ocean. The Cenozoic collision between Africa and Europe reactivated the normal faults from the synrift phase causing the formation of the Atlas Mountains. The External Rif zone associated with the Alpine Orogeny developed during the Oligocene into the Miocene from a combination of the slow but continuous convergence between Africa and Eurasia. It is characterized by deformed fold and thrust belts that give the domain its distinct arc shape.

A variety of data and an evaluation of previous studies were assembled to complete an extensive look at a region of the External Pre-Rif. We have analyzed a proprietary 5 km grid of gravity data and six seismic reflection lines. The High Atlas and Rif ranges both exhibit low gravity anomalies that have been explained by a variety of processes including delamination and typical Airy isostacy. Preliminary modeling shows the crustal thickness ranging from approximately 28 km along the Moroccan coastline to 36 km beneath the High Atlas. Seismic data offers a glimpse at the complex structure associated with the inversion of the Atlas rift into the Atlas Mountains. Seismic ray tracing models depict the reflection lines ability to image the complex structure.