in the Saint Elias Orogen: Motivation for Research
Ronald L. Bruhn, Dept. Geology and Geophysics, University of Utah
Salt Lake City, UT 84112-0111 (rlbruhn@mines.utah.edu)
The tectonics of terrane collision and accretion in the
Saint Elias orogen poses fundamental questions concerning the evolution of
southern Alaska and mountain belts in general. Problems concerning the
interaction between tectonics, erosion and exhumation, glacial processes, and
sedimentation provide much of the motivation for the workshop. In this poster I want to focus on an
additional and equally important motivation – namely that the orogen is an active analog for
tectonic processes that formed much of the North American Cordillera as well as
other mountain belts around the globe, and the orogen is also an important site
to study the relationships between structural geology and the generation of
large to great magnitude earthquakes. Recent geological work onshore has
started to refine the spatially and temporally complex history of deformation
and structural development related to collision and accretion of the Yakutat
terrane. Future work on neotectonics will require detailed mapping and dating
of faulting and folding episodes, including Quaternary deformation.
Furthermore, the close relationship between the courses of glaciers and major
tectonic boundaries begs the question as to how those are related and what are
the implications for focusing deformation as well as erosion? This problem will
require integration of data from quantitative remote sensing, onsite
measurements of glaciers and geological structures, as well as geodynamic
measurements of the spatial patterns and rates of deformation. Furthermore,
there is substantial evidence to suggest that collision, accretion and partial
subduction of the Yakutat terrane affects the tectonics of most of southern
Alaska including deformation in Cook Inlet forearc basin, volcanism in the
Wrangell Mountains, creation of a structurally complex subduction zone, and
structural linkages to the Totschunda and Denali fault systems in the
interior. Understanding how stresses are applied to, and then dissipated
within, the North American plate will provide crucial insight into the
fundamentals of continental margin tectonics, distributions of earthquakes and,
ultimately, hazards posed by earthquakes. Lessons learned by studying active
deformation in the Saint Elias orogen and elsewhere in southern Alaska has both
important and sobering implications for studies of ancient continental margin
orogen belts, particularly for those who attempt to relate structural patterns
to plate motions.
[Note the ideas expressed above have evolved while working with my colleagues T.L. Pavlis, G. Plafker, A.L.J. Ford, R.R. Forster, P.J, Haeussler, and L. Serpa]