Abstract
The Variscan middle crust of the eastern Pyrenees is represented by the Belesta and Caramany gneissic units of the North Pyrenean Agly Massif. In this study, we date and reinterpret the orthogneisses and granites composing these units. We characterize a recurrent plutonic activity spanning all the Paleozoic in this part of the Pyrenean crust. The Belesta unit (amphibolite facies) is mainly composed of sills of (Latest Ediacaran)–Earliest Cambrian (542 ± 4 and 540 ± 4 Ma) orthogneisses (70% of the series), almost unknown in the Pyrenees until now, and Latest Carboniferous–(Earliest Permian) (307 ± 3–298 ± 3 Ma time span) granites (15% of the series). These plutonic rocks were emplaced in probably Ediacaran aluminous pelites later transformed into paragneisses (15% of the series). The Caramany unit (granulite facies) is mainly composed of Precambrian aluminous paragneisses migmatized during the Latest Carboniferous–(Earliest Permian) (299 ± 4 Ma), sills of Earliest Cambrian (529 ± 5 Ma) orthogneisses and sills (about 30% of the series) of Late Carboniferous (308 ± 3–299 ± 3 Ma) opxbearing and opx-free granodiorites, grt-bearing leucogranites and norites. Among these last rocks, the Ansignan charnockite, forming a 800 m-thick laccolith near the base of the Caramany unit, and previously dated at 314 ± 6/7 Ma (Respaut, Lancelot, Neues Jahrbuch Miner Abh 147-1:21–34, 1983), is refined at 307 ± 3 Ma. Our results confirm the importance of the Late Carboniferous plutonism in deep levels of the Pyrenean crust, which largely resulted from recycling of older para- and orthoderived rocks of this crust. The emplacement of hundreds of metres in thickness of granites and other plutonic rocks in the Variscan Pyrenees occurred in a rather short time both as sills in these deep levels and as large plutons in shallower levels, a fact which necessarily had consequences on the HT–LP Carboniferous metamorphism.
Highlights
The evolution of the deep parts of modern chains may hardly be studied, because the crust cannot be observed directly and the stages of this evolution, for instance the emplacement of plutonic rocks, are very slow phenomena
The Pyrenean range (Fig. 1a) was formed by the Late Cretaceous–Eocene collision of the Iberian and European plates, but a large part of this chain is constituted by Precambrian and Paleozoic metamorphic and plutonic rocks which represent remnants of the upper and middle crust of the West European Variscan orogen
We characterize and date the various plutonic events which occurred during the Variscan orogeny but during all the Paleozoic times, taking the North Pyrenean Agly massif as a case study, because Paleozoic rocks are largely exposed and represent a natural cross section from the base of the middle crust to the upper crust
Summary
The evolution of the deep parts of modern chains may hardly be studied, because the crust cannot be observed directly and the stages of this evolution, for instance the emplacement of plutonic rocks, are very slow phenomena. Deeply eroded, may provide specific data related to their evolution (e.g., Linnemann et al 2008; Lardeaux 2014; Couzinié et al 2017) Even when such data are available, unraveling the various events which characterized this evolution is complicated, because precise ages of all the rocks constituting the crust are often unknown. The Pyrenean range (Fig. 1a) was formed by the Late Cretaceous–Eocene collision of the Iberian and European plates, but a large part of this chain is constituted by Precambrian and Paleozoic metamorphic and plutonic rocks which represent remnants of the upper and middle crust of the West European Variscan orogen These formations are suitable for addressing the question of the crust evolution by successive emplacements of plutonic rocks. We characterize and date the various plutonic events which occurred during the Variscan orogeny but during all the Paleozoic times, taking the North Pyrenean Agly massif as a case study, because Paleozoic rocks are largely exposed and represent a natural cross section from the base of the middle crust to the upper crust
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