Reconstructing a Super-Eruption From the Upper Ordovician Period in the Eastern Pyrenees, Spain

Abstract

The Pyrenean basement rocks, NE of the Iberian Peninsula, southwestern Europe, include evidence of several pre-Variscan magmatic episodes which indicate the complex geodynamic history of this segment of the northern Gondwana margin from late Neoproterozoic to Early-Palaeozoic times. One of the most significant magmatic episodes was late Mid-early Upper Ordovician (Darriwilian-Katian) age that produced several granitic bodies and volcanic rocks interbedded with Sandbian-Katian sediments. This magmatism is well represented in the Ribes de Freser area (Freser valley, Bruguera and Campelles localities, eastern Pyrenees), where these Ordovician magmatic rocks were affected by an irregularly distributed Variscan deformation and mainly by severe Alpine tectonics, which originated the superposition of several structural units. We present a palinspatic reconstruction of this Alpine deformation (80-20 Ma), that permitted us to infer the geometry, facies distribution, original position, thickness, and significance of these volcanic rocks. This reconstruction allows us to interpret the volcanic rocks cropping out at the Freser valley, Bruguera, and Campelles areas as intra-caldera deposits representing a minimum preserved volume of the order of 100 km3. This may confirm the existence of super-eruptions of Upper-Ordovician age in that sector of the eastern Pyrenees and emphasizes the extent of the Upper-Ordovician felsic volcanism in this sector of the northern Gondwana margin, probably developed in an extensional scenario linked to the development of the Rheic Ocean during Gondwana margin breakup.