Show simple item record

dc.contributor.authorWildland, Alec D.
dc.date.accessioned2022-12-20T23:30:17Z
dc.date.available2022-12-20T23:30:17Z
dc.date.issued2022-08
dc.identifier.urihttp://hdl.handle.net/11122/13094
dc.descriptionThesis (M.S.) University of Alaska Fairbanks, 2022en_US
dc.description.abstractUnderstanding the relationship of accreted terranes with pericratonic North America is critical for unraveling the complex, polydeformational history of the North American Cordillera. The Cordillera represents a multi-accretionary system that has been fundamentally active since the Jurassic. The allochthonous Yukon-Tanana Terrane is an extensive and heterogeneous accreted terrane in the northern Cordillera. The tectonic boundary separating the Yukon-Tanana Terrane from pericratonic North America is exposed in eastern Alaska and is defined by a northward-dipping and low-angle ductile shear zone. This shear zone is interpreted to have exposed the structurally lower assemblages of parautochthonous North America during top-to-the-southeast directed exhumation in the Cretaceous. This interpretation is based on muscovite, biotite, and hornblende metamorphic cooling ages (ca. 100-120) of amphibolitefacies rock samples collected within the parautochthon. Historically, ⁴⁰Ar/³⁹Ar thermochronology has been a major resource, along with quartz c-axis petrofabric analysis, in identifying the boundaries of the shear zone. However, temporal relationships between shear zone formation, exhumation, and magmatism have remained incompletely understood. Targeted geologic mapping and petrochronology using a more robust chronometer, such as monazite, can aid these previous radiometric and kinematic interpretations. U-Th-Pb monazite petrochronology of samples within and outside the shear zone have placed better constraints on the age of shearing and exhumation. These analyses and observations support that exhumation of the parautochthonous assemblages occurred during the Cretaceous. Additionally, the ductile shear zone which facilitated juxtaposition of allochthonous and parautochthonous assemblages was active ca. 108 Ma. The northern Cordillera is also home to widespread Cretaceous, voluminous, and metallogenically important magmatism in both Alaska and the Yukon Territory. U-Pb zircon geochronology analyzed from 12 mid-Cretaceous plutons has better refined the crystallization history of these granitic bodies (ca. 115-100 Ma). Together, the monazite and zircon geochronology show that the shear zone and granitic plutons are linked, and that top-to-the-southeast crustal extension placed both spatial and temporal controls on the emplacement of mid-Cretaceous magma.en_US
dc.language.isoen_USen_US
dc.subjectShear zonesen_US
dc.subjectStructural geologyen_US
dc.subjectIntrusionsen_US
dc.subject.otherMaster of Science in Geoscienceen_US
dc.titleTemporal links between ductile shearing, widespread plutonism, and tectonic exhumation near the boundary of parautochthonous and allochthonous terranes in the northern Cordillera, Alaskaen_US
dc.typeThesisen_US
dc.type.degreemsen_US
dc.identifier.departmentDepartment of Geosciencesen_US
dc.contributor.chairRegan, Sean
dc.contributor.committeeNadin, Elisabeth
dc.contributor.committeeJones, James V. III


Files in this item

Thumbnail
Name:
Wildland_A_2022.pdf
Size:
9.644Mb
Format:
PDF

This item appears in the following Collection(s)

Show simple item record