Comparative geochemical study on Furongian–earliest Ordovician (Toledanian) and Ordovician (Sardic) felsic magmatic events in south-western Europe: underplating of hot mafic magmas linked to the opening of the Rheic Ocean

Abstract

Abstract. A geochemical comparison of early Palaeozoic felsic magmatic episodes throughout the south-western European margin of Gondwana is made and includes (i) Furongian–Early Ordovician (Toledanian) activities recorded in the Central Iberian and Galicia–Trás-os-Montes zones of the Iberian Massif, and (ii) Early–Late Ordovician (Sardic) activities in the Eastern Pyrenees, Occitan Domain (Albigeois, Montagne Noire and Mouthoumet massifs) and Sardinia. Both phases are related to uplift and denudation of an inherited palaeorelief, and stratigraphically preserved as distinct angular discordances and paraconformities involving gaps of up to 22 million years. The geochemical features of the predominantly felsic Toledanian and Sardic activities point to a predominance of magmatic byproducts derived from the melting of metasedimentary rocks, rich in SiO2 and K2O and with a peraluminous character. Zr ∕ TiO2, Zr ∕ Nb, Nb ∕ Y and Zr vs. Ga ∕ Al ratios, and rare-earth element (REE) and εNd(t) values suggest the contemporaneity, for both phases, of two geochemical scenarios characterized by arc and extensional features evolving to distinct extensional and rifting conditions associated with the final outpouring of mafic tholeiite-dominant lava flows. The Toledanian and Sardic magmatic phases are linked to neither metamorphism nor penetrative deformation; on the contrary, their unconformities are associated with foliation-free open folds subsequently affected by the Variscan deformation. The geochemical and structural framework precludes subduction-generated melts reaching the crust in a magmatic arc-to-back-arc setting and favours partial melting of sediments and/or granitoids in the lower continental crust triggered by the underplating of hot mafic magmas related to the opening of the Rheic Ocean.

Tectonic architecture of the northern Dora-Maira Massif (Western Alps, Italy): field and geochronological data

“…The Ordovician granitic and rhyolitic magmatism is well known all over the southern part of the Variscan belt from northern Spain (Talavera et al, 2013 ), Western France (Ballèvre et al, 2012 ), to the Pyrenees (Navidad et al, 2018 ), Sardinia (Cruciani et al, 2013 ) and the Alps (Bergomi et al, 2017 ; Chen et al, 2023 ; Gilotti et al, 2023 ). Although part of this magmatism is older than the ages we have obtained for the Granero Orthogneiss, and also for the Muret Orthogneiss, similar Upper Ordovician ages are recorded in the Pyrenees, the Montagne Noire and Sardinia (see Stephan et al, 2019 , and Álvaro et al, 2020 , for a review). The diversity of metasediments in the Dora-Maira polycyclic basement reflects a long history, partly deciphered thanks to the detrital zircon geochronology.…”

A window into an older orogenic cycle: P–T conditions and timing of the pre‐Alpine history of the Dora‐Maira Massif (Western Alps)

“…A major episode of granitic to rhyolitic magmatism occurred throughout the northern Gondwana palaeomargin during the Ordovician. The protolith of the Muret orthogneiss may represent one of the latest manifestations of this episode, although its early Silurian age (c. 440 Ma) is slightly younger than the main episode recorded in nearby areas (c. 460 Ma) (Alvaro et al, 2020; Ballèvre et al, 2012; Pouclet et al, 2017). The Muret orthogneiss is the only Early Palaeozoic granitoid known so far in the Internal Crystalline Massifs.…”

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

“…Nonetheless, in Sardinia the felsic volcanism started earlier: it ranged from the Furonginan or Tremadocian to the Katian [67-69, 71, 73], and in contrast with the Pyrenees, Ordovician felsic plutonic rocks are subsidiary. We interpret that the Upper Darriwilian-Sandbian volcanism reported here represents the final pulse of an Ordovician tectonothermal event, which in the Pyrenees started with the Floian-Darriwilian emplacement of plutonic rocks [75]. This event belongs to the Cambrian-Ordovician voluminous magmatism that occurred along the northwestern Gondwanan margin of continental Europe [see review in 76].…”

“…This event belongs to the Cambrian-Ordovician voluminous magmatism that occurred along the northwestern Gondwanan margin of continental Europe [see review in 76]. Several genetic models have been proposed to explain this magmatism, from subductionrelated melts [69,73,[77][78][79][80], to post-collisional decompression melting without significant mantle involvement [81], or partial melting of the lower continental crust in response to either mafic underplating or mafic intrusion [34,43,75,[82][83][84] or asthenospheric upwelling [31,85,86]. The example described here, with thick volcano-related deposits controlled by fault activity, fits better with an extensional setting, also compatible with the extensional faults of the same age described in the Canigó massif [43] and with the drastic changes in thickness and facies of the El Baell and Estana formations.…”