Collaborative Research:
ST. Elias Erosion/Tectonics Project (STEEP)
This is a multi-disciplinary
study to address the evolution of the highest coastal mountain range on
Earth - the St. Elias Mountains of southern Alaska and northwestern
Canada. This orogen has developed over the past few million years as
the Yakutat block,
a continental-oceanic terrane, has attempted subduction beneath the
eastern end of
the Aleutian arc-trench system. The ~500 km-long, 150 km-wide St. Elias
mountain
range is the product of the dynamic balance between rapid uplift
induced by crustal
convergence and rapid exhumation by a regional system of large,
fast-moving temperate
glaciers. Most sediments are deposited either on a broad shelf or in
deepsea fans and
provide a complete record of the tectonic, climatic, erosional, and
eustatic events
that have accompanied the orogeny. The overarching goal of the project
is to develop
a comprehensive model for the St. Elias orogen that accounts for the
interaction of
regional plate tectonic processes, structural development, and rapid
erosion. The focus
of the study is on the partitioning of deformation within the system
from upper mantle
flow to near-surface faulting and exhumation. The study will
investigate the geodynamics
of oblique collision under a set of conditions that will allow the PIs
to address several
important and fundamental questions:
Fundamental Questions
1. Has intense
Quaternary glacial erosion
redistributed mass in the orogen sufficiently to change regional
deformational patterns,
and has focused erosion along deep glacial valleys been sufficient to
localize crustal
strains?
2. How is deformation partitioned into lithospheric shortening and
uplift versus
lateral extrusion of the detached crust, and does intense erosion
influence this partitioning?
3. Is the orogeny driven primarily by subduction of a buoyant oceanic
plateau or by collision
of a small microcontinental block attached to allochthonous ocean crust?
Addressing
these
questions has broad implications for understanding the geodynamics of
oblique collision in
general, the role of different mechanisms in development of far-field
orogenic effects, and
the control of erosion on development of slip partitioning during
oblique convergence. The
project also has general implications for how subduction/accretion of
small continental
terranes versus oceanic plateaus contribute to deformation of the
continents, and ultimately
the fate of these fragments in construction of the crustal collage
which is typical of
virtually all continents. Specifically, the P.I.s propose a
multidisciplinary approach
involving seismologists (subsurface imaging and seismicity),
geologists, geodesists,
glaciologists, geochronologists, and geodynamic modelers.
Photo: Malaspina Glacier, 1966, NSIDC/WDC for Glaciology, Boulder, compiler. 2002, updated 2006. Online glacier photograph database. Boulder, Colorado USA: National Snow and Ice Data Center/World Data Center for Glaciology. Digital media.