serie NOVA TERRA nº 48

margin of Gondwana was a passive and extended

one. The first collision occurred in the Early De-

vonian (before

400–390 Ma) and caused deep

subduction of a section of the margin of Gond-

wana and the generation of a HP–UHP meta-

morphic belt (Upper Allochthon of the Variscan

suture). Lateral motion between Gondwana and

Laurussia favoured the opening of a relatively

wide pull-apart basin at

400–395 Ma. The rap-

id closure of this basin started at

380 Ma and

caused the accretion of buoyant oceanic litho-

sphere of Devonian age below the northern con-

tinent. This oceanic lithosphere is represented by

the most common ophiolites found in the Vari-

scan Belt (Upper Ophiolitic Units). Mafic slices

with a similar age and showing greenschist facies

recrystallization were accreted later, followed by

mafic complexes with Cambrian age generated

by the activity of peri-Gondwanan volcanic arcs

that progressively reached the collision zone as

the basin shrank (Lower Ophiolitic Units). Final-

ly, further convergence led to a new collision with

another section of the Gondwanan margin, with

generation of a second HP–LIT belt at

370 Ma

(Basal Units). Convergence continued during the

Carboniferous and produced the complex intra-

continental deformation that characterizes the

Variscan belt. According to structural data and

paleogeographic reconstructions for the alloch-

thonous pile of NW Iberia, the Devonian and

Carboniferous convergence was accompanied by

a dextral lateral component for most of the time.

8. TWO STAGE COLLISION

204