An ensialic volcanic arc along the northwestern edge of Palaeotethys—Insights from the Mid‐Triassic volcano‐sedimentary succession of Ivanščica Mt. (northwestern Croatia)

Abstract

This work aims to unveil the origin, geodynamic significance, and diagenetic history of pyroclastites and associated chert documented within the Upper Anisian volcanosedimentary succession of the Ivanščica Mt. in Central Europe. An abundance of pyroclastic material points to polyphase volcanic activity and deep-water sedimentation along the rim of an oceanic realm. Radiolarian-based dating revealed Illyrian age of chert intercalated with pyroclastites. The latter are largely vitro-crystalloclastic and were emplaced as airborne tuff. The crystalloclasts of sanidine, plagioclase, altered pyroxene, and amphibole are principal tuff constituents merged in the altered glassy matrix consisted of palagonite, clay minerals, and calcite. Variations in alteration assemblages reflect an extensive in situ eogenesis in an open hydrologic system that gradually evolved toward a restricted fluid percolation environment. Mineralogy, chemistry, and occurrence of andesitic tuff clearly denote an explosive volcanic activity formed at the top of suprasubduction zone. Such scenario presumes a complex genesis outlined in following steps: (a) partial melting and dehydration of down-going Palaeotethyan slab which gave rise to the subduction-related magmatism {LILE, Th, and LREE [(La/Lu) cn = 6.51−9.42] enrichment; negative anomalies of Nb-Ta, P, and Ti [e.g., (Nb/La) n = 0.31−0.44]}; (b) magma contamination via interaction with continental crust during magma uplift along tectonically weakened zones of upper crust [positive Pb spikes, negative ε Nd (−4.18 to −4.44), and 147 Sm/ 144 Nd ≤ 0.113175]. This is in favour of geodynamic evolution that hypothesizes the existence of an active, ensialic, and mature volcanic arc developed along the southern active continental margins of Euramerica (Laurussia) during Late Anisian subduction of Palaeotethyan lithosphere.

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

“…Similar effusive and pyroclastic rocks found elsewhere in the mountains of NW Croatia are all interbeded with Middle Triassic marine sediments (e.g. Goričan et al, 2005;Halamić, 1998;Marci et al, 1982Marci et al, , 1984Šimunić and Šimunić, 1979;Šimunić, 1992;Slovenec et al, 2020). The volcanic activity of that period was characterized by submarine andesite to basaltic lava flows accompanied by multiple explosive eruptions of volcanic material.…”

“…The Middle Triassic volcanism of NW Croatia is represented by submarine flows of basaltic to rhyolitic lavas and explosive eruptions of pyroclastic material (e.g. Goričan et al, 2005;Šimunić, 1992;Slovenec et al, 2020;and references therein). Previous stratigraphic studies identified two volcanic events.…”

“…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.…”

“…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). The subduction and back-arc extension processes in the Alpine-Carpathian-Dinaride realm produced diverse magmatisms, among which the calc-alkaline one dominated (e.g.…”

“…One exception is a recent study on the Upper Anisian volcano-sedimentary succession of Mt. Ivanščica by Slovenec et al (2020) that reports the origin, geodynamic significance, and diagenetic history of pyroclastics and associated chert.…”