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| Titel |
Numerical model of continental collision: comparison between Variscan (Bohemian Massif) and modern (Himalayan) orogeny |
| VerfasserIn |
P. Maierová, O. Cadek, K. Schulmann, O. Lexa |
| 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 |
250067986
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| Zusammenfassung |
| Internal structure and dynamics of modern orogens are still uncertain, because
geophysical methods provide only indirect information and geological observation is
limited due to preservation of a rigid crustal lid. In contrast to this, the internal
structure of ancient orogens can be directly studied at the surface, as the crustal lid
is eroded during the final stage of an orogeny. An example of a well preserved
ancient orogen is the Bohemian Massif consolided during the Variscan orogeny. For
this orogen, a scenario of tectonic evolution has been established involving crustal
thickening and growth of a topographic plateau, vertical extrusion of lower crust (in
the Moldanubian domain) and subsequent subhorizontal channel flow above an
inclined margin of a continental promontory. The Variscan orogeny was in spatial and
time extent similar to the Himalayan orogeny and detailed comparison between the
two systems shows further analogies in metamorphism, geometry of collisional
process, and felsic middle/lower crustal composition which has been proposed in some
regions.
We present results of 2D numerical modeling of continental collision, which we
performed using the FE software Elmer (www.csc.fi/english/pages/elmer). For this
purpose, we extended the software by procedures for compositional convection,
visco-plastic deformation, erosion, sedimentation and flexural isostasy. The model
well reproduces the main geological observables for the continental collision in
the Bohemian Massif: Timing of the exhumation of the lower crust and related
pressure-temperature paths, the subhorizontal flow, and topography evolution and
sedimentation. The salient feature of the model is presence of the felsic heat-productive lower
crust in the Moldanubian block. Not all sets of model parameters lead to efficient
extrusion of the rocks to the surface. For the development of the subhorizontal flow,
focusing effect of erosion is essential. Applied slope-dependent erosion focuses
the flow to the steep front of the orogen while erosion at the orogenic plateau is
small.
We then compare Bouguer anomaly and surface heat flow in our model with those
measured for active orogens. The gravity anomaly in the model is built up progressively
during crustal thickening and vertical mass transfer stages and remains stable during the
subhorizontal flow stage. The anomaly has a similar shape but somewhat smaller magnitude
(about -350 mGal) than the one of the Himalayan orogen. The heat flow grows during the
building of the plateau up to about 90 mW/m2, and evolves into a narrow positive
anomaly above the front of the orogen during subhorizontal extrusion of rocks to the
surface. |
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