serie NOVA TERRA nº 48

Provenance of the

Variscan Upper Allochthon

5.1. Introduction

5.2. Partial conclusions

5.3. Article

5.1. Introduction

This chapter presents an article dealing

with provenance studies of the Cariño Gneiss

formation. These gneisses represent the

intermediate-pressure (IP) Upper Allochthon in

the Cabo Ortegal Complex. The main objective

of this article is to find out fromwhich continents

or cratons the detrital materials of the upper units

derive. Back in 2003, an article was published

dealing with these issues, studying the upper units

from the Órdenes Complex (Fernández-Suárez

., 2003). This work already concluded that these

units are derived from Gondwana but even so

this article was planned with the aim of knowing

if the Upper Allochthon is in fact a continuous

terrane present in the rest of the complexes. It was

also required to refine the conclusions proposed

increasing the statistical adequacy of the data by

analysing more zircon grains with the U–Pb LA-

ICP-MS zircon method and to complement the

study with Lu–Hf zircon and Sm–Nd whole-rock

analyses. With these additional techniques many

conclusions have arisen about crustal growth

events in the detrital source areas and about the

geological environment of the depositional basin.