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VIII
Two-stage collision:
Exploring the birth of Pangea
in the Variscan terranes
8.1. Introduction
8.2. Partial Conclusions
8.3. Article
8.1. Introduction
This article is presented to englobe the Upper
Allochthon in the general context of continental
interaction in the process of Pangea´s amalga-
mation. In the Allochthonous Complexes there
are two high grade terranes with continental af-
finity that underwent subduction, the Upper Al-
lochthon (upper units) and the Basal Allochthon
(basal units). A modern analogue is shown to
address the conditions of the initial stages of the
continental assembly.
8.2. Partial conclusions
The subduction event that both terranes un-
derwent is not one, but two events with different
ages and P–T conditions. The subduction of the
Upper Allochthon terrane reached HP–HT or
even ultra-HP–HT conditions and it is
c
. 30 Ma
older than the subduction of the Basal Alloch-
thon, which registered HP and low-to-interme-
diate-T (HP–LIT). In this article it is proposed
that the volcanic arc system that in a broad sense
the Upper Allochthon represents did not drift
away from Gondwana to form the Rheic Ocean
in its wake, but instead a relatively small ba-
sin was formed, now represented by the Lower
Ophiolitic Units. Between the formation of the
magmatic arc and the Devonian subduction the