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The AAPG/Datapages Combined Publications Database

AAPG Special Volumes


Pub. Id: A115 (1992)

First Page: 259

Last Page: 281

Book Title: M 53: Geology and Geophysics of Continental Margins

Article/Chapter: Structural and Tectonic Evolution of Oceanic Crust within the Jurassic Quiet Zone, Offshore Morocco: Chapter 14: African and Mediterranean Margins

Subject Group: Geologic History and Areal Geology

Spec. Pub. Type: Memoir

Pub. Year: 1992

Author(s): James S. Holik, Philip D. Rabinowitz


The results of extensive MCS and sonobuoy reflection and refraction data are analyzed in order to determine the oceanic crustal structure and evolution in the Jurassic Quiet Zone off northwest Africa between 30 and 35°N. Within a zone characterized by a broad bathymetric arch, a unit, which we estimate is Late Cretaceous in age, with diffracted upper surface and chaotic seismic facies (UCF) is observed between sedimentary units of continuous and parallel seismic character. Results from CDP Previous HitvelocityNext Hit spectra analysis define a Previous HitvelocityNext Hit inversion between the UCF (4.7 km/sec) and the underlying sediments (3.1 km/sec). A deep crustal layer with velocities of 7.1-7.4 km/sec rather than the typical layer 3 Previous HitvelocityTop of 6.8 km/sec is observed in the sonobuoy refraction measurem nts. A good spatial correlation exists between this zone of high crustal velocities and the extent of the UCF implying a common origin for these features. The movement of Africa relative to the Canary hot spot, which can explain these phenomena and is consistent with stratigraphically derived ages, allows us to interpret the UCF as volcanic in origin. Within the framework of the hot-spot model, the UCF is evidence for a volcanic overprint on the region. Data off the conjugate margin of Nova Scotia were examined and a similar overprint was not found. These observations indicate that the evolution of these two margins differed at some time in their history and is consistent with the concept of the passage of a hot spot that rejuvenated the ancient crust off Morocco commencing approximately 60 MYBP.

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