GEODYNAMICS OF THE MENDOCINO TRIPLE JUNCTION
Kevin Furlong
Geodynamics Research Group
Department of Geosciences, Penn State University
Rob Govers
Vening Meinesz Research School of Geodynamics
Faculty of Earth Sciences, Utrecht University
Poster Presentation: EGS 1999
Background
As the North American crust interacts with
the Migrating Mendocino Triple Junction,
the crust is first significantly thickened and
then equivalently thinned over a distance of
a few hundred kilometers (within a time
frame of 5 Ma or less). This process of
ephemeral crustal thickening is proposed
to result from viscous coupling between the
northward migrating Gorda (Juan de Fuca)
slab and the base of North America south of
the triple junction.
Generalized geophysics of the Mendocino Triple
Junction region (MTJ). Heavy red dashes outline
region of thickened crust, determined from
reflection/wide-angle and regional tomography.
Isostatic residual gravity anomaly encloses
gravity low ( 50 mgal) determined by Jachens
and Griscom (1983).
Schematic model of crust/mantle interactions at MTJ.
South of triple junction asthenospheric mantle upwells
to fill space vacated by migrating Gorda Slab. Rapid
cooling of emplaced mantle creates a viscous coupling
among the exposed edges of the Gorda and Pacific plates
and the exposed underside of the North American crust.
Migration of the Gorda plate drives deformation within the
North America crust.
Observed crustal structure from reflection/wide-angle(left)
(Beaudoin et al. 1996) and tomography (Villasenor et al., 1998).
Region of maximum crustal thickening sits astride the southern
edge of the subducted Gorda slab. Patterns of seismicity indicate
a reduction in seismicity in the thickened crust (translation zone)
while regions of active thickening/thinning show higher levels of
seismic activity.
Modeling
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