Revelation of the Thermal History of nearly Metamict Zircon of the Taza-Guercif Basin (Morocco) using Scanning Electron Microscope High-density Fission-track (SEM-HDFT) Dating

Tyler M. Izykowski
University of South Carolina, Columbia, SC

Standard zircon fission-track (ZFT) 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 ZFT 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 10⁷ tracks/cm², making it difficult to analyze very old and very high-uranium content zircon grains.

Herein, I employ a new technique, which 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 (Variscan) 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.

AAPG Search and Discovery Article #90181©2013 AAPG/SEG Rocky Mountain Rendezvous, University of Wyoming, Laramie, Wyoming, September 27-30, 2013