Geological constraints on the Paleozoic tectonic evolution of tectonostratigraphic terranes in the Iberian Massif

Abstract

The presence of oceanic Paleozoic sequences in the Iberian Variscan Fold Belt is used to identify and separate suspected exotic terranes from a reference Iberian Autochthon Terrane which constitutes the greater part of it. In this paper the relevant data characterizing the pre-accretionary evolution of the Paleozoic Iberian Terranes are presented, as well as the available evidence concerning the accretionary process itself. Emphasis is placed on the analysis of the sedimentary, igneous and structural expression of the major events which affected the Iberian terranes before, during and after their amalgamation. The main conclusions of such an analysis may be summarized as follows: 1. (a) recognition of rift and passive margin stages in all the Iberian Massif terranes during the Early Paleozoic; 2. (b) Late Paleozoic accretion of the exotic terranes to the Iberian Autochthon via a long and complex process (Variscan Orogeny) which involved initial subduction underneath the latter and eventual obduction, followed by oblique collision of a promontory (the Iberian Autochthon northwestern margin) with a northwestern continental block. This latter process could account for the large-scale crustal imbrication shown by the northern branch of the orogen, coeval with predominant strike-slip faulting in the southern branch, as well as with the formation of the typical arcuate shape of this orogenic belt. Major present uncertainties relate to the palinspastic provenance of continental suspect terranes and their correlation with similar units in other circum-Atlantic Paleozoic orogens. A discussion and speculations on this subject are dealt with in the final section of this paper.