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|Title: ||Tardi-Variscan Deformation in Ibero-Moroccan Sector; Implications on Pangeia Assemblage|
|Authors: ||Dias, Rui|
|Keywords: ||Variscan orogeny|
|Issue Date: ||16-Sep-2013|
|Publisher: ||Department of Earth & Environmental Sciences, KU Leuven, Belgium|
|Citation: ||DIAS, R., MOREIRA, N., RIBEIRO, R., HADANI, M. & ALMEIDA, P (2013) Tardi-variscan Deformation in Ibero-Moroccan Sector; Implications on Pangeia Assemblage, 19th International Conference on DEFORMATION MECHANISMS, RHEOLOGY & TECTONICS, Leuven, Belgium, p. 40.|
|Abstract: ||The tardi-Variscan structures in the Ibero-Moroccan domain show a brittle-ductile behaviour,
overlapping the earlier main ductile stages, developed in the same orogenic process. The interaction
between tectonic thickening, erosion and isostasy during the progressive colisional stages of the Variscan
Wilson cycle was responsible by this rheological evolution. The tardi-Variscan deformation can not be
understood without recognize the role of the first-order anisotropies. These anisotropies could be either
the result of main Variscan events or inherited from previous tectonic cycles. Previous works (e.g. Arthaud
& Matte, 1977) emphasize the crucial role of major E-W lithospheric anisotropies in the development of
the tardi-Variscan fracture pattern.
Recent structural detail mapping in Portugal (in SW sector of Iberian Chain) and Morocco (in Anti-Atlas
and Western High Atlas) shows kinematic and geometric similarities between tardi-Variscan structures in
both sectors. Indeed, this deformation event is characterized by left-lateral NNE-SSW to NE-SW brittleductile
shear zones; these shears can be observed from orogenic scale (e.g. Vilariça or Messejana Faults in
Iberia and Snaâla-Oulmés one in Morocco) to regional scale. At the regional scale, the shears are expressed
by decametic-hectometric faults with metric to decametric offsets.
The absence of a right-lateral conjugate family and the common presence of orogenic dextral E-W
shear zones, support a dominoes genetical model to the sinistral NNE-SSW shears (Ribeiro, 2002). These
dominoes were driven by the major E-W lithospheric anisotropies. Indeed, although the left-lateral shears
are pervasive at minor scales the E-W dextral shears (e.g. Azores-Gibraltar Fault on transition between
Iberian and Morocco segments or in Morocco region Tizi'n Test and Tantan shears) could only be seen at
the scale of the Ibero-Moroccan domain.
This model extrapolates to whole Ibero-Moroccan domain a previous proposal to the Iberian segment
(Ribeiro, 2002). This is a variant of the classic model suggested for tardi-Variscan faulting (e.g. Arthaud &
Matte, 1977). Such model considers a major dextral simple shear between Gondwana and Laurussia, which
induce a conjugate system of strike-slip faults. However, this hypothesis is not consistent with field
observations, because the sinistral shear family clearly predominates and its dextral conjugate is absent.
Moreover, in last stages of Pangeia collision, it could be emphasized a dextral transcorrent system between
Laurussia and Gondwana (e.g. Nance et al, 2012). This is in agreement with recent paleogeographic models
proposed to the last stages of Variscan Orogeny.|
|Appears in Collections:||CGE - Comunicações - Em Congressos Científicos Internacionais|
GEO - Comunicações - Em Congressos Científicos Internacionais
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