Triassic magmatism in the European Southern Alps as an early phase of Pangea break-up

Abstract

Magmatic rocks from the Dolomites, Carnic and Julian Alps, Italy, have been sampled to investigate the origin and geodynamic setting of Triassic magmatism in the Southern Alps. Basaltic, gabbroic and lamprophyric samples have been characterized for their petrography, mineral chemistry, whole-rock major and trace elements, and Sr, Nd and Pb isotopic compositions. Geothermobarometric estimates suggest that the basaltic magmas crystallized mostly at depths of 14–20 km. Isotopic data show variable degrees of crustal contamination decreasing westwards, probably reflecting a progressively more restitic nature of the crust, which has been variably affected by melting during the Permian period. Geochemical and isotopic data suggest that the mantle source was metasomatized by slab-derived fluids. In agreement with previous studies and based on geological evidence, we argue that this metasomatism was not contemporaneous with the Ladinian–Carnian magmatism but was related to previous subduction episodes. The lamprophyres, which likely originated some 20 Ma later by lower degrees of melting and at higher pressures with respect to the basaltic suite, suggest that the mantle source regions of Triassic magmatism in the Dolomites was both laterally and vertically heterogeneous. We conclude that the orogenic signatures of the magmas do not imply any coeval subduction in the surrounding of Adria. We rather suggest that this magmatism is related to the Triassic rifting episodes that affected the western Mediterranean region and that were ultimately connected to the rifting events that caused the break-up of Pangea during the Late Triassic – Early Jurassic period.

Mantle-derived Corundum-bearing Felsic Dykes May Survive Only within the Lower (refractory/inert) Crust: Evidence from Zircon Geochemistry and Geochronology (Ivrea-Verbano Zone, Southern Alps, Italy)

“…Important igneous events mark the geodynamic evolution of the area now referred to the Southern Alps during Triassic times. In particular, a diffuse igneous activity with orogenic, shoshonitic to K-rich calc-alkaline, affinity developed during the Middle Triassic (~243-235 Ma) in the Eastern (Dolomites area) and Central (Brescian PreAlps) sectors ( [127,128,129,130,131,132]. These events occurred under mainly transtensional regime, which determined the partial melting of mantle regions metasomatised by crustal components during the Variscan orogenic cycle [129,130,131].…”

“…In particular, a diffuse igneous activity with orogenic, shoshonitic to K-rich calc-alkaline, affinity developed during the Middle Triassic (~243-235 Ma) in the Eastern (Dolomites area) and Central (Brescian PreAlps) sectors ( [127,128,129,130,131,132]. These events occurred under mainly transtensional regime, which determined the partial melting of mantle regions metasomatised by crustal components during the Variscan orogenic cycle [129,130,131]. In the westernmost sector of the Southern Alps, the record of this tectono-magmatic activity is poorly documented, being essentially limited to Ladinian-Carnian ages provided by magmatic (e.g., 239-232 Ma; [60,63,133]) and metamorphic zircons, e.g., [134,135] from the deepest crustal rocks of IVZ, namely those of the Finero Complex, and by zircons from tuffitic layers occurring in the carbonate platform (241 Ma; [132,136]).…”

Middle Triassic high-K calc-alkaline effusive and pyroclastic rocks from the Zagorje-Mid-Transdanubian Zone (Mt. Kuna Gora; NW Croatia): mineralogy, petrology, geochemistry and tectonomagmatic affinity

“…pyroclastic material as well as rare intrusive rocks mark this magmatic event (e.g. Bianchini et al, 2018;Bonadiman et al, 1994;Casetta et al, 2018;Castorina et al, 2020;Lustrino et al, 2011Lustrino et al, , 2019De Min et al, 2020;Saccani et al, 2015;Sloman, 1989;Slovenec et al, 2020;Storck et al, 2018;Trubelja et al, 2004;and references therein). The Middle Triassic magmatism has been related to the formation of the Adriatic-Dinaridic carbonate platform(s) and its subsequent disintegration (e.g.…”

“…Yet, the geodynamic framework and tectonomagmatic evolution of the area separating Gondwana and Laurasia (the Southern Alps, Dinarides, Hellenides, and the Alpine-Carpathian Belt) remain controversial (e.g. Bortolotti and Principi, 2005;Bortolotti et al, 2013;De Min et al, 2020;Neubauer et al, 2019;Şengör, 1984;Stampfli and Borel, 2004;Stampfli et al, 2013;Zulauf et al, 2018). The magmatism of the Middle to Upper Triassic period has been related to compressional, extensional and/or transtensional geodynamic processes (e.g.…”

“…Two hypotheses have emerged over the years i) that the continental rifting caused the magmatic events (e.g. Aljinović et al, 2010;Crisci et al, 1984;Harangi et al, 1996;Knežević et al, 1998;Kovács, 1992;De Min et al, 2020;Pamić, 1984;Pamić and Balen, 2005;del Piaz and Martin, 1998;Saccani et al, 2015;Velledits, 2004Velledits, , 2006; and references therein) and ii) that the magmatism was originated by convergent plate movements triggered by the subduction of the Paleotethys lithosphere (e.g. Bébien et al, 1978;Bianchini et al, 2018;Bonadiman et al, 1994;Casetta et al, 2018;Cassinis et al, 2008;Castellarin et al, 1980Castellarin et al, , 1988Castorina et al, 2020;Grimes et al, 2015;Kovács, 1992;Obenholzner, 1991;Schmid et al, 2004;Slovenec et al, 2020;Smirčić et al, 2018;Borel, 2002, 2004;Storck et al, 2019;Trubelja et al, 2004;Zanetti et al, 2013;and references therein).…”