Origin and duration of late orogenic magmatism in the foreland of the Variscan belt (Lesponne — Chiroulet — Neouvielle area, French Pyrenees)

Abstract

During the late stage of the Variscan orogeny, the pyrenean segment underwent intense magmatism and regional high temperature-low pressure metamorphism. In the Lesponne-Chiroulet-Neouvielle area, a granodioritic pluton was emplaced in the upper crust while dioritic to granitic magmas were emplaced in metamorphic domes. Magmatism was contemporaneous with the regional crustal partial melting recorded in the core of the domes. The area is therefore a key target in the Pyrenees to discuss potential magmatic sources as well as the age and duration of the late Variscan magmatism. Geochemical data on representative magmatic rocks highlight two distinct sources of magma: a mantle source and a metasedimentary crustal source that produced respectively metaluminous and peraluminous magmas. Geochronological results show that magmatism took place over a period of about 10 My from ca. 303 to ca. 290 Ma. During this period, the middle to lower crust was composed of partially molten metasediments intruded by mantle and crustal magmas that crystallized in a final pulse at ca. 290 Ma. Late Variscan metamorphism and magmatism recorded in the Pyrenees have to be related to a significant and rapid heating from the underlying mantle rather than to crustal processes such as the maturation of a thickened continental crust. We propose that the initiation of metamorphism and bimodal magmatism at ca. 305 Ma in the Pyrenees is the expression of the delamination of the Gondwanan lithospheric mantle at a global scale in the Variscan belt.

Tectono-sedimentary evolution of a rift system controlled by Permian post-orogenic extension and metamorphic core complex formation (Bidarray Basin and Ursuya dome, Western Pyrenees)

“…The latest Carboniferous and earliest Permian (305-295 Ma) was a period of intensive reorganization of the collapsed Variscan belt in which mantle delamination led to the formation of several post-orogenic oroclines (e.g., Weil et al, 2010;Gutiérrez-Alonso et al, 2012). Our study suggests that the formation of the Ursuya MCC and Bidarray graben reflects the switch from dominant N-S convergence recorded in the Pyrenean Axial Zone from 310 to 290 Ma (during oroclinal bending; see Denèle et al, 2014;Cochelin et al, 2017;Lemirre et al, 2019) to overall E-W extension in the Pyrenean realm.…”

“…Formed in an overall context of N-S horizontal shortening, these domes are elongated parallel to the regional direction of stretching in the middle and lower crust, like Journal Pre-proof J o u r n a l P r e -p r o o f 7 "a-type" MCCs (Cochelin et al, 2017(Cochelin et al, , 2018b. Deposition of the earliest thin volcaniclastic sediments occurred in the Pyrenees synchronously with ductile flow within these gneiss domes (e.g., compare the ages obtained by Pereira et al, 2014, andLemirre et al, 2019).…”

“…In this orogenic context, the Pyrenees were located in the foreland of the Variscan belt and were mainly affected by late Variscan HT-LP metamorphism due to lithospheric mantle delamination (Denèle et al, 2014;Cochelin et al, 2017;Lemirre et al, 2019 and references therein). This metamorphism occurred between 310 and 290 Ma (see Denèle et al, 2014;Lemirre et al, 2019;Poitrenaud et al, 2019) and was responsible for partial melting of the middle and lower crust, which then intruded into the base of the upper crust of the Axial Zone as gneiss domes in compressional settings ( Fig. 1; Denèle et al, 2007;2009;Cochelin et al, 2017Cochelin et al, , 2018aCochelin et al, , 2018b.…”

Sedimentology and U-Pb dating of Carboniferous to Permian continental series of the northern Massif Central (France): Local palaeogeographic evolution and larger scale correlations

“…Subsequent nappe-stacking was accompanied by the progressive exhumation of HP-LT metamorphic rocks (Bosse et al, 2000;Pitra et al, 2010;Ducassou et al, 2014), during the early Carboniferous. Next, between the late Carboniferous and the early Permian, post-orogenic extension is recorded by the formation of high-grade metamorphic domes associated with detachment faults, such as the Velay (Ledru et al, 2001) or the Montagne Noire (Van Den Driessche and Brun, 1991;Poujol et al, 2017) domes in the Massif Central, the Lesponne and Chiroulet domes in the Pyrenees (Lemirre et al, 2019) or in the Quiberon and Sarzeau areas (Gapais et al, 2015), in the Armorican Massif. This extensive event is often attributed to the post-orogenic collapse of a thickened and hot crust (Ménard and Molnar, 1988;Echtler and Malavieille, 1990).…”

Anisian granodiorites and mafic microgranular enclaves in the eastern Kunlun Orogen, NW China: Insights into closure of the eastern Paleo–Tethys

“…Accretionary orogens preserve important records of continental growth through multiple subduction and collision events involving arc–arc, arc‐continent and continent‐continent assembly (Xiao et al, ; Xiao, Windley, Hao, & Zhai, ). Voluminous granitoids, some of them carrying mafic microgranular enclaves (MME) formed during different stages of subduction, collision and post‐collisional extension are widely distributed in accretionary orogens, such as those in the Appalachian orogen (Whalen et al, ), the Variscan orogen (Lemirre, Cochelin, Duchene, Blanquat, & Poujol, ; Moita, Santos, Pereira, Costa, & Corfu, ), and the Central Asian Orogenic Belt (Ma, Chen, Zhao, Qiao, & Zhou, ; Yuan et al, ; Zhou et al, ), among others. The MMEs hosted by the granitoids in these regions represent either xenoliths captured from country rocks (Maas, Nicholls, & Legg, ), residual material that unmixed from the host melt (Chappell, White, & Wyborn, ), early formed crystals from the parental magma or cognate fragments of cumulate minerals (i.e., cumulates) (Donaire, Pascual, Pin, & Duthou, ), or products of mixing of magmas derived from different sources (Baxter & Feely, ; Q. Chen et al, ; Ma et al, ; Zhou et al, ).…”