New late Middle to early Late Ordovician U–Pb zircon ages of extension-related felsic volcanic rocks in the Eastern Pyrenees (NE Iberia): tectonic implications

Joan Martí,Josep Maria Casas,Martim Chichorro,Luigi Solari

doi:10.1017/s0016756819000116

Abstract

AbstractPre-Variscan basement rocks from the Pyrenees provide evidence of several magmatic episodes with complex geodynamic histories from late Neoproterozoic to Palaeozoic times. One of the most significant episodes, consisting of several granitic and granodioritic bodies and volcanic rocks, mostly pyroclastic in nature, dates from the Late Ordovician period. In the Eastern Pyrenees, this magmatism is well represented in the Ribes de Freser and Núria areas; here, the Núria orthogneiss and the Ribes granophyre, both dated at c. 457–460 Ma, seem to form a calc-alkaline plutonic suite emplaced at different crustal levels. The presence of numerous pyroclastic deposits and lavas interbedded with Upper Ordovician (Sandbian–lower Katian, formerly Caradoc) sediments, intruded by the Ribes granophyre, suggests that this magmatic episode also generated significant volcanism. Moreover, the area hosts an important volume of rhyolitic ignimbrites and andesitic lavas affected by Alpine deformation. These volcanic rocks were previously attributed to late Variscan volcanism, extensively represented in other areas of the Pyrenees. Here we present the first five laser-ablation U–Pb zircon dates for this ignimbritic succession and two new ages for the Ribes granophyre. The ages of the ignimbrites, overlapping within error, are all 460 Ma, suggesting a genetic relationship between the plutonic and volcanic rocks and indicating that the Sandbian–Katian magmatism is much more voluminous than reported in previous studies, and possibly includes mega-eruptions linked to the formation of collapse calderas.

Highlights

The Pyrenees are a WNW-ESE trending Alpine fold and thrust belt that contains pre-Variscan basement rocks, late Neoproterozoic-to-Carboniferous in age
In some cases, where there is a lack of fossils and of reference stratigraphic horizons, the w geochronological data enable us to assess the age of the pre-Middle Paleozoic metasedimentary sequences and correlate them along the whole margin (Padel et al 2017)
We present new geochronological results that demonstrate these rocks correspond to a late Middle to early Upper Ordovician magmatic event rather than a late Palaeozoic one

Summary

Introduction

The Pyrenees are a WNW-ESE trending Alpine fold and thrust belt that contains pre-Variscan basement rocks, late Neoproterozoic-to-Carboniferous in age. In some cases, where there is a lack of fossils and of reference stratigraphic horizons, the w geochronological data enable us to assess the age of the pre-Middle Paleozoic metasedimentary sequences and correlate them along the whole margin (Padel et al 2017) This is the case for the preUpper Ordovician sequences of the eastern Pyrenees where Ediacaran, Ordovician and Carboniferous magmatic rocks are interbedded with or mainly intrude into an almost unfossiliferous thick In this study we focus on a thick sequence of strongly welded, rheomorphic (i.e: showing secondary flow structures) rhyolitic ignimbrites that crop out extensively in the Campelles-Bruguera area, along the southern slope of the Canigó massif, (Fig. 1) These volcanic rocks were initially attributed to Upper Carboniferous-Lower Permian magmatism (Robert, 1980), lying unconformably on an undated pre-Variscan slate-dominated succession (Cambrian-Ordovician?; Muñoz, 1985).

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Conclusion