Date of Award
Master of Science (MS)
Northward transport of the Yakutat terrane along the Transition and Queen Charlotte-Fairweather transform faults led to Neogene collision of the Yakutat terrane with the southern continental Alaska margin. Northward translation resulted in a stratigraphy that records the erosion of thermotectonic terranes along its path. The strata of the Yakutat terrane includes the Lower Oligocene to Lower Eocene Kulthieth Formation, the Upper Eocene to Lower Miocene Poul Creek Formation and the Miocene-Pleistocene Yakataga Formation. Detrital zircon fission-track (DZFT) ages from stratigraphically coordinated samples collected in the Northern Robinson Mountains yield provenance information of the units that can shed light on their transport history. For all dated samples 50 grains were counted and morphology/color noted and grain ages were deconvolved into component populations. The Kulthieth Formation has three primary cooling age populations at ~70-97 Ma, 38-58 Ma and 28-31 Ma. The Poul Creek Formation has three primary cooling age populations at ~61-67 Ma, 39-42 Ma and 24-33 Ma. The Yakataga Formation has three primary cooling age populations at ~68-77 Ma, 30-35 Ma and 15-21 Ma. The DZFT grains were then analyzed by LA-ICPMS to determine U/Pb crystallization ages. For the Yakataga Formation three crystallization peak age populations resulted: ~52 Ma, ~71 Ma and ~155 Ma. For the Poul Creek Formation four crystallization peak ages resulted: ~59 Ma, ~71 Ma, ~94 Ma, and ~147 Ma. Three grains yielded U/Pb ages of ~318 Ma, ~365 Ma, ~1864.71 Ma. Analysis of the Kulthieth Formation resulted in three U/Pb crystallization age populations of ~59 Ma, ~94 Ma, and ~159 Ma.
Paleocene to Eocene deposition of the Yakutat terrane stratigraphy records a long-lived, non-volcanic source terrain that crystallized from ~50-220 Ma and cooled from ~48-110 Ma. Miocene cooling episodes in the Kulthieth and the Poul Creek Formations likely records deposition associated with plutons located in the northern Coast Plutonic Complex and the Kuiu-Etoilin belt in the North American Cordillera. Late Miocene deposition of the Yakataga Formation records a provenance signal of crystallization from ~50-53 Ma and cooled from ~17-20 Ma. Late Miocene deposition is likely associated with the Chugach accretionary complex and superimposed Sanak-Baranof Plutonic Belt (~50-58 Ma).
The uniform provenance of the Kulthieth and Poul Creek Formations, the overall grain-age distribution, and the distinct lack of volcanic zircons favors northern reconstructions (i. e. Plafker et al., 1994) for the original position of the Yakutat terrane. Southern options (i.e. Bruns, 1982), can be ruled out mainly due to the lack of volcanic grains that would be expected in the stratigraphy during continuous transport of the terrane along route.
Perry, Stephanie Ellen, "Thermochronology and provenance of the Yakutat terrane, southern Alaska based on fission-track and U/Pb analysis of detrital zircon" (2006). Geology Theses and Dissertations. 68.
Appendix 1 - Zeta Calculations, Fluence Calculations, Irradiation Order
perrymstxtax2.pdf (2840 kB)
Appendix 2 - Fission Track Ages
perrymstxtax3.pdf (1167 kB)
Appendix 3 - Detrital Zircon Fission Track Grain Characteristics
perrymstxtax4.pdf (2029 kB)
Appendix 4 - Binomial Peak-fit Ages
perrymstxtax5.pdf (40235 kB)
Appendix 5 - Digital photographs taken of individual zircon grains for the double-dating procedure