30 / 352
and subduction of transitional crustal sections to
high/ultra-high-P depths (
c.
400 Ma), followed
by exhumation and subsequent generation of
ephemeral supra-subduction or pull-apart oce-
anic basins (
c.
395 Ma), finally closed during
the second event of collision and restarted sub-
duction of the Gondwana margin to the North
(
c.
370 Ma). According to this model the Upper
Units of NW Iberia would represent the lower
plate to the Rheic Ocean suture.
Introduction
Most of the pre-Alpine basement in central
and western Europe is formed by the Variscan
Orogen. This belt can be followed from Iberia,
across Brittany and the French Massif Central,
to the Bohemian Massif, also extending towards
the basement of the Alps, Corsica and Sardinia
(Fig. 1). The orogen was linear in origin, but it
was affected by several late to post-orogenic
oroclinal bends that hinder correlations across
the belt and the understanding of some critical
questions about its origin and evolution through
time (Matte, 2001: Martínez Catalán, 2011; Weil
et al.
, 2012). It is flanked by two different low-
grade thrust belts, a foreland thrust belt to the
South represented by the Cantabrian Zone of the
Iberian Massif, and an external thrust belt to the
North and West forming the Rhenohercynian
and South Portuguese zones (Fig. 1). The external
limits of these thrust belts, both to the South and
North, define a doubly vergent Variscan orogenic
front.
The Variscan Orogen has continuity in eastern
North America in the Appalachian-Alleghanian
Belt. This long orogen was developed during
the main stages of the Pangea assembly which
occurred by the collision of two large continents,
Gondwana to the South and Laurussia to the
North. It is considered that the final assembly
of Pangea occurred in Carboniferous and
14
3. GEOLOGICAL FRAMEWORK
Fig. 1.
Terranes and oroclines of the Variscan belt (Martínez Catalán, 2011). Arcs: BA, Bohemian; CIA, Central Iberian;
IAA, Ibero-Armorican; MCA, Massif Central. Zones of the Iberian Massif: CIZ, Central Iberian; CZ, Cantabrian; GTMZ,
Galicia-Trás-os-Montes; OMZ, Ossa-Morena; SPZ, South Portuguese; WALZ, West Asturian-Leonese. Shear zones and
faults: BCSZ, Badajoz-Córdoba; JPSZ, Juzbado-Penalva; LPSZ, Los Pedroches; NPF, North Pyrenean; PTSZ, Porto-Tomar;
SISZ, Southern Iberian. Location of the geological map and section presented in Fig. 2 is shown.