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| Titel |
Geodynamic modeling of passive margin systems from tectonic reconstructions with deforming plate boundaries |
| VerfasserIn |
S. Williams, N. Flament, C. Heine, M. Hosseinpour Vazifehshenas, M. Seton, M. Gurnis, R. D. Müller |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250064673
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| Zusammenfassung |
| The effect of mantle flow on surface topography has been the subject of considerable interest
over the last few years. A common approach to the problem is to link plate tectonic
reconstructions and global geodynamic models. An important limitation of this approach is
that traditional plate tectonic reconstructions do not take the deformation of the lithosphere
into account. We introduce quantitative models of surface plate kinematics that include areas
of deforming continental crust. We present a series of global reconstructions including
deforming plates in key areas, derived using tools developed within the open source plate
modeling software GPlates.
In traditional plate reconstructions, the continents are represented as rigid blocks that overlap
in full-fit reconstructions. Models that use topological polygons avoid continental overlaps,
but plate velocities are still derived on the basis of Euler poles for rigid blocks. To resolve
these issues, we use a methodology that requires at minimum two inputs; (1) the relative
motions of the rigid blocks within continents; (2) a definition of the regions in which
continental crust deformed between these blocks. We use geological and geophysical data to
interpret the landward limit of significant extension and crustal thinning along conjugate
passive margins. These boundaries are used to construct polygons along both margins that
define the extent of the stretched continental crust on either side of the rift. We derive
individual motion histories for each point on the conjugate continent/ocean boundaries
(COBs). Joined together, these COB points form the topological boundaries of
deforming domains in which each vertex moves independently. The deforming
domains represented by topological meshes extend forward in time as the major
rigid plates drift apart. In our tectonic reconstruction with deforming plates, the
timing and the intensity of continental extension is imposed by the progressive,
diachronous breakup and initiation of seafloor spreading for each major margin
system.
The velocity field derived from the plate reconstructions is used as a time-dependent surface
boundary condition in mantle convection models that include compositionally distinct crust
and continental lithosphere embedded within the thermal lithosphere. In deforming
areas, the velocity field is obtained by linearly interpolating velocities from adjacent
non-deforming areas within GPlates. We computed forward global mantle flow
models using 3D-spherical finite-element code CitcomS to simultaneously quantify
the relative contributions of lithospheric stretching, thermal subsidence, and deep
mantle flow to the subsidence of passive margins. Applied to the South Atlantic, the
method reproduces the first-order asymmetry of the margins. In particular, the large
subsidence of the Argentinian margin is due to the dynamic topography induced by
ongoing subduction along the narrow southern portion of South America. This result
illustrates the importance of dynamic topography to the total subsidence at passive
margins. |
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