Date of Award

1-1-2013

Document Type

Open Access Dissertation

Department

Earth and Ocean Sciences

Sub-Department

Geology

First Advisor

David L Barbeau

Abstract

Northwest Africa provides unique insight into a wide range of geologic processes throughout a vast portion of Earth's history. Moroccan geology in particular can provide valuable insight, from the formations of West Africa through the Eburnian orogeny (~2000 Ma), Gondwana during the Pan-African orogeny (~900-500 Ma), and Pangaea by means of the Hercynian (Variscan) orogeny (~400-300 Ma), to more recent crustal and climatic events, such as the Messinian salinity crisis (5.96-5.33 Ma). However, the current lack of western literature regarding this region presents a significant obstacle in understanding the aforementioned processes. Herein, I employ a new technique in zircon fission-track dating, a thermochronological tool that has proved integral in understanding tectonic and sedimentary systems, in order to provide new insight into the ancient and recent geologic past of northern Morocco.

Standard zircon fission-track dating is a powerful tool for understanding source- to-sink systems; that is, the tracing of sediment from its original source, or provenance, through initial erosion, ensuing transport, and ultimate deposition in sedimentary basins. However, conventional, optically based fission-track analysis has historically been limited in application due to the densities of fission-tracks that can be counted with the ~1500x magnification ceiling of optical microscopes. Standard fission-track dating has an upper limit of approximately 2 x 10^7 tracks/cm^2, making it difficult to analyze very old and very high-uranium content zircon grains. The present advancement in fission-track analysis incorporates the increased magnification of scanning electron microscopy to reconstruct the long-term thermal history of basin sediments of the Taza-Guercif basin, located in the South Rifean Corridor of Morocco. Highly damaged zircon grains were selected to evaluate the low temperature (~200-300°C) thermal histories of basin sediments as well as the two most proximal and likely sediment sources. Two significant cooling age populations were revealed at 607 Ma and 319 Ma, likely relating to the Pan- African and Hercynian Orogenies, respectively. The absence of a more recent cooling age population suggests a relatively long period (at least 300 Myr) of thermal quiescence in the Western Mediterranean, despite being in an active convergence zone with numerous tectonothermal events, namely Neogene Betic-Rif Alpine metamorphism.

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