Date of Award:
Master of Science (MS)
John W. Shervais
The Farmington Canyon Complex, situated along the Wasatch front in northern Utah, has been the target for many studies. The FCC has been interpreted to be a passive margin sedimentary wedge. Previous studies have yielded isotopic ages that broadly support an Archean age of formation, and a prominent mid-proterozoic amphibolite grade metamorphic event. Based on this study, a new interpretation for the FCC is presented. Field relations and whole-rock geochemistry as well as recent advances in understanding Archean crustal processes have resulted in the FCC to be considered as an accretionary complex that formed along the SW margin of the Wyoming province in the early Archean. Rock assemblages such as mafic and ultramafic metavolcanics have chemistries that resemble oceanic crust and arc related volcanics. The extensive quartzo-felspathic gneiss and schist units have compositions that reflect greywacke, and are presented here as a melange matrix. The quartzites have chemistries, which may represent cherts or silicified microbial mats. The field relations and timing of these rocks indicate that the FCC may represent a continental arc synchronous with the closing of an ocean basin, forming an accretionary wedge. This culminated with the mid-proterozoic metamorphic event as this continental arc collided with the Santaquin arc, as well as the SW margin of Laurentia. This amphibolite grade metamorphic event has subsequently reset or overprinted isotopic evidence and obscured any textures that may have existed. Although much has yet to be learned about Archean processes, comparison to other recognized Archean accretionary complexes has yielded striking similarities, and it is presented here that the FCC represents an active margin, and is likely an accretionary melange.
Andreasen, Kyle C., "Does the Southern Farmington Canyon Complex Record a late Archean/Early Proterozoic Accretionary Complex?" (2007). All Graduate Theses and Dissertations. 6753.
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