Repeated lithospheric-scale reactivation of an inherited plate boundary in the eastern Alaska Range, Alaska, USA

• Main Author: Waldien, Trevor
• Other Authors: Roeske, Sarah M
• Format: Thesis
• Language: English
• Published: eScholarship, University of California 2021
• Subjects: Geology; Alaska; Lithosphere; Reactivation; Strike-slip; Suture; Tectonics; alaska range; Yukon
• Online Access: https://escholarship.org/uc/item/2926d9qr; https://escholarship.org/content/qt2926d9qr/qt2926d9qr.pdf

Accretionary orogens, such as the North American Cordillera, form by repeated collisions of allochthonous oceanic and continental fragments (terranes). Due to the closure of ocean basins that is required for far-traveled terranes to become part of the orogen, fault systems at the boundaries of allochthonous terranes commonly form as plate boundaries and experience multiple phases of reactivation after collision. The repeated phases of reactivation along the terrane-boundary fault systems often mask the earlier deformation events and lead to uncertainty regarding the location of the main lithospheric-scale geologic boundary between terranes. In this dissertation, I present the geologic evolution of the master reactivated plate boundary structure in the Alaska Range suture zone of southern Alaska. In the first chapter, I use detailed geologic mapping, structural analysis, U-Pb and 40Ar/39Ar geochronology, geochemistry of spinel-group minerals, and receiver function seismology to parse metamorphic rocks in the suture zone. With these methods, I show that the main suturing structure is located along the boundary between amphibolite grade schists and gneisses associated with North America in the north and greenschist grade metagreywacke and slate associated with allochthonous oceanic terranes in the south. The main suturing structure was reactivated after ca. 32 Ma and nucleated an imbricate thrust system that progressed southward. I argue that reactivation along the boundary between the metasedimentary belts is the third phase of activity on this structure, owing to the penetration of that boundary through the lithosphere. In the second chapter, I use regional geologic mapping, U-Pb and 40Ar/39Ar geochronology, Hf isotope analysis, and statistical tests to confirm the correlation between Alaska Range suture zone metamorphic rocks in the Alaska Range and hypothesized correlative metasedimentary and plutonic belts in southwestern Yukon Territory. After confirming the correlation, I use the correlative rock packages to ...