Geodynamic Framework for the Tectonic Trigger of Late Neogene Deformation in Southern Alaska

点击翻译按钮获取中文摘要

Various aspects of Late Neogene tectonics in southern Alaska, such as uplift along a weak transpressional boundary or transfer of plate boundary stresses to the continental interior, have been studied individually at other active margins. The superposition of these processes in southern Alaska provides a unique opportunity to quantify the relative importance and interaction of tectonic driving forces and plate structure using 3-D geodynamic models. This project has two components. The first part focuses on determining how pre-existing structural features (the slab shape, plate boundary coupling, narrow lithospheric-scale weak zones, and regional strength contrasts) interact to transfer and localize deformation in the continental interior. The results from the first part of the project provide the context in which to ask: What triggered the uplift of the Alaska Range 5 to 6 million years ago? This second part of the project tests two hypotheses for the tectonic trigger: a change in Pacific Plate motion or collision of the Yakutat Terrane, a small oceanic plateau that is currently accreting to and subducting in the Aleutian Trench. Predictions from 3-D time-dependent models are compared with the observational constraints on the timing and location of uplift of the Alaska Range and the regional distribution of deformation. This work will provide the first three-dimensional geodynamic model with which to test geologic hypotheses for the recent tectonic evolution of southern Alaska, and makes testable predictions for the onset of deformation in regions surrounding the Alaska Range where there are fewer observational constraints. The theory of plate tectonics assumes that interiors of plates are rigid and relative motion between plates occurs through deformation in a narrow plate boundary region. However, on continental margins that are under compression or extension, the regions of deformation can be broad or narrow, but far from the plate boundary. This study uses the observed deformation in southern Alaska to learn which structures in the continent determine the character of the deformation and will, consequently, broaden understanding of deformation in other convergent margins around the world. Three-dimensional visualization of the results are being integrated into undergraduate courses to teach students how to view and interpret complex three-dimensional structures and in public outreach activities. Planned displays at Denali National Park will incorporate simulation movies from this project.