6. Rotational kinematics of the Boltaña anticline - Instituto Geológico ...

Boltaña kinematics Mochales, 2011
2.1. Introduction
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2. The Pyrenean Orogen
The North Atlantic opening and the subsequent clockwise rotation of the African plate during
Cretaceous and Tertiary times produced a general compression along the Tethys margins. In its
western side, the Pyrenees, Iberian Range and the Betics-Rift underwent lower shortening related to
this geodynamic process in comparison to eastern areas (Alps, Figure 1). During the Alpine orogenic
stage, intraplate compressional stresses controlled basin inversion, crustal thickening and lithospheric
folding. Variably deep crustal roots characterize the Alpine orogenic chains (Ziegler and Dèzes,
2006).
According to some reconstructions, four hundred km of shortening took place between the
Iberian and Eurasian plates in the Pyrenean domain during the opening of the Bay of Biscay (from 118
to 80 M.a., Sibuet et al., 2004). The ECORS seismic reflection profile and teleseismic data show the
presence of two distinct slabs dipping to the north. The southern slab is associated to the subduction of
the neo-Tethys Ocean, which was formed from late Jurassic to early Aptian (Figure 2). Coevally,
elongated back arc basins formed along the future Pyrenean domain (Sibuet et al., 2004). The northern
one, active from 85 M.a. is linked to the subduction of the lower continental crust located south of the
Pyrenean domain. In the upper crust, normal faults and the north Pyrenean fault became reverse faults
and former arc basins were inverted, originating the uplift of the Pyrenees as a double verging wegde
(Sibuet et al., 2004), figure 2.
By means of up-to date kinematic data, based on magnetic anomalies in the Atlantic ocean, a
geodinamic model of the relative motions of Africa-Iberia and European plates was proposed (Figure
3, Rosenbaum et al., 2002). Convergence of Africa with respect to Europe commenced between 120 to
83 M.a. This motion depended on fluctuations in convergence rates characterised by two periods of
relatively rapid convergence (Late Cretaceous and Eocene-Oligocene times) alternated with periods of
relatively slower convergence (during the Paleocene and since the Early Miocene). Several stages of
Iberian-Europe plate kinematics can be recognised (Figure 3): 1) Left-lateral strike-slip motion in Late
Jurassic-Early Cretaceous; 2) Late Cretaceous convergence; 3) Paleocene quiescence; 4) Short period
of right lateral strike-slip motion; 5) Final Eocene-Oligocene convergence (Rosenbaum et al., 2002).