EUROPROBE News 9
SW-IBERIA
Transpressional Orogeny in the Variscides
by Antonio Ribeiro (Lisbon), David Sanderson (Southampton)
and SW-Iberia colleagues
The Variscan orogen in southwestern Iberia offers a unique opportunity to
image and study a transpressional orogen and to examine the partitioning of deformation in
3-dimensional space and time. The region consists of a series of zones representing
different tectonostratigraphic units exposed at a variety of structural levels. Varying
components of shortening and left-lateral strike-slip deformation have been recognised
from field studies and from geodynamic models, such as the indentor model of the
Ibero-Armorican arc. Studies of the structure, stratigraphy, metamorphism, magmatism and
palaeogeography will allow a reconstruction of the geometry and history of this important
class of orogens produced by oblique collision of lithospheric plates.
The principal aim of this multidisciplinary project is to better
understand orogeny resulting from oblique collision. This will be achieved by imaging the
crust at different structural levels through collaborative work on existing data,
geological and geophysical investigations of critical areas and acquisition of new seismic
reflection profiles through the orogen. The seismic profiles will be fully integrated with
the surface geology and provide images deep into the mantle, thus, providing a critical
'missing link' in the imaging of the Variscan orogen in Europe.
Within the Variscan of SW-Iberia are some of Europe's most important
Volcanic Massive Sulphide ore deposits (Rio Tinto, Neves-Corvo, etc.). The tectonic
setting and reconstruction of the ore bodies requires detailed stratigraphical and
structural studies; this project will provide new concepts for further exploration.
The SW-Iberia project will focus on the following main goals:
Imaging of the
lithosphere using deep seismic reflection profiling, wide-angle studies, magnetotelluric
and other geophysical experiments.
Testing of
transpressional models through mapping of strain variation through the different
structural zones. This, together with the geophysical imaging will allow testing of
thick-skinned versus thin-skinned models of deformation, and constrain estimates of
shortening and displacement at crustal and lithospheric scales.
Reconstruction of
the pre-collisional (North Gondwanan) and syn-collisional palaeogeography of the crustal
units using sedimentary, faunal and palaeomagnetic studies to constrain the timing and
position of orogenic processes.
Examination of the
boundaries (sutures) and associated rocks (high grade metamorphics and ophiolites), in
order to constrain the processes of continental collision.
Examination of the
origin, setting and timing of magmatism and metallogenesis to constrain emplacement
mechanisms and crustal evolution.
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