Death of super-continents and birth of oceans heralded by discrete A-type granite igneous events: the case of the Variscan-Alpine Europe

Abstract

Granitoids occupy large areas of the Variscan-Alpine Europe. The specific group of A-type granites identifies postcollisional (post-orogenic) and anorogenic geodynamic settings. Post-orogenic igneous provinces are emplaced during the very last episodes of supercontinent amalgamation. Anorogenic igneous provinces accompany continental break-up and predate the development of new oceanic basins. Though not voluminous compared with the other granite types, A-type granites substantiate critical periods of the life of supercontinents. Their ages of emplacement in the Variscan-Alpine Europe span the entire Cambrian-Triassic time interval. They are not random, however, and correspond to discrete episodes. Two major age groupings, both with a c. 60 My duration, are distinguished. The Early Cambrian-Early Ordovician period corresponds to Pannotia amalgamation, followed by its break-up and the development of the Rheic-Proto-Tethys Ocean. The Late Carboniferous-Early Triassic period corresponds to Rheic closure and Pangaea amalgamation, followed by its break-up and the development of the NeoTethys Ocean. Devonian-Early Carboniferous A-type igneous episodes, scarce in Europe but widespread in Central Asia, accompanied the development of the Palaeo-Tethys Ocean.

The petrogenesis of anorogenic felsic magmas and AMCG suites: Insights on element mobility and mutual cryptic contamination from polythermal experiments

“…As Bonin (2008) correctly stated, no one has ever seen a migmatite in which the leucosome has the mineral assemblage and composition of a typical A-type granite or syenite. That is one reason for Martin's (2006) suggestion, not for partial melting, but rather closeto-complete melting of a suitably metasomatized precursor.…”

“…Such a scenario differs fundamentally from closedsystem anatexis resulting from prograde metamorphism of the crust, which does undoubtedly apply broadly to cratonic masses around the world (Sawyer, 2008). Having edited Sawyer's book, I can vouch for Bonin's (2008) assessment that A-type leucosome in regionally developed migmatites is simply not found.…”

Permian A-type granites of the Western Carpathians and Transdanubian regions: products of the Pangea supercontinent breakup

“…The A-type granites represent ferroan and anhydrous magmatic suites, typically developed in post-orogenic or anorogenic tectonic environments. Several genetic concepts have been proposed for the origin of their magma, including the processes of anatexis, fractionation and remelting (± metasomatism) of various (meta)igneous crustal or mantle sources (e.g., Collins et al 1982;Clemens et al 1986;Eby 1990;Creaser et al 1991;Patiño Douce 1997;Bonin 2004Bonin , 2007Bonin , 2008Martin 2006;Lu et al 2020).…”

“…The A-type granites were originally distinguished by Loiselle and Wones (1979) as a specific group of granitic rocks with peculiar chemistry and geotectonic setting (e.g., Bonin 2007Bonin , 2008. The A-type granites' origin is generally connected with an extensional regime in the lithosphere (Collins et al 1982;Whalen et al 1987;Bonin 2007) and it is related to the geodynamic settings, which are consistent with both crustal and mantle sources (Bonin 2004;Shellnutt and Zhou 2007;Grebennikov 2014;Lu et al 2020, and references therein).…”

Astrophyllite-alkali amphibole rhyolite, an evidence of early Permian A-type alkaline volcanism in the western Mongolian Altai

“…7a), and Y (93-109 ppm; Fig. 7b), as well as the elevated 10000×Ga/Al ratios of 5.1 and 5.8 indicate an A-type affinity for the rhyolite (Whalen 1987;Bonin 2008).…”