Magma–sediment interaction during the emplacement of syn-sedimentary silicic and mafic intrusions and lavas into and onto Triassic strata (Circum-Rhodope Belt, northern Greece)

Abstract

Within the Circum-Rhodope Belt in northern Greece, Middle Triassic neritic carbonate metasediments are locally intercalated with quartz-feldspar-phyric metarhyolites. In the same belt, Upper Triassic pelagic lime-marl-layered metasediments are similarly intercalated with low-grade metamorphosed basalt, dolerite and minor andesite and trachydacite. We interpret these sequences as due to magmatism active during the rifting event that eventually led to the opening of the Vardar Ocean. Despite the overprint of Late Jurassic deformation and low greenschist metamorphism, peperitic textures produced by magma-wet sediment interaction are well preserved at the contacts between the silicic volcanic rocks and the originally wet unconsolidated neritic carbonate sediments, suggesting contemporaneous magmatism and sedimentation. The mafic and intermediate volcanic rocks lack peperitic textures at their contacts with the pelagic sedimentary rocks. Thin margin parallel banding in the sedimentary members of the sequence indicates thermally affected original contacts with the mafic volcanic rocks only locally and at a microscopic scale. The absence of peperite in this case is attributed to the consolidated state of the sediments at the time of the mafic magma emplacement.Key words: Triassic, Circum-Rhodope Belt, contact metamorphism, low greenschist metamorphism, carbonate sediments, basalt and dolerite, rhyolitic peperites. be inferred about their origin. Peperites were formed where a quartz-feldspar-phyric partly extrusive rhyolitic crypto-dome and rhyolitic sills intruded Triassic neritic carbonate sediments. Descriptions of the newly recognized peperite occurrences are provided. Specific criteria to discriminate peperite from other mixed volcanic-sediment breccia facies are discussed. Where mafic and intermediate rocks are in contact with Triassic pelagic sediments, peperite is absent; instead, small scale contact metamorphic phenomena are present. The cause of the absence of peperite in this case is discussed.

Peperites

“…The formation of peperites, which occurred by the interaction of lava with wet sediment, is a vitally significant environmental indicator. Nonetheless, few examples of this phenomenon have been comparatively documented, which happened during Archean successions (Beresford, et al, 2002;Wilson and Grant, 2006;Moulton, et al, 2011;Barnes and Van Kranendonk, 2014;Barnes and Arndt, 2019); Proterozoic succession (McPhie, 1993;Rawlings, 1993;Biske, Romashkin and Rychanchik, 2004;Sinha, et al, 2011;Constenius, et al, 2017); Palaeozoic succession (Brooks, 1995;Doyle, 2000;Cas, et al, 2001;Chen, et al, 2013;Zhu, et al, 2014;Chen, et al, 2016;Memtimin, et al, 2020;Bann, Jones and Graham, 2022); Mesozoic succession (Wilson, 1991;Wilson, 1993;Hanson and Hargrove, 1999;Templeton and Hanson, 2003;Hanson and, Nemeth, Breitkreutz and Wilke, et al, 2004;Palinkaš, et al, 2008;Asvesta and Dimitriadis, 2013;Krobicki, et al, 2019); Cenozoic succession (Erkül, Helvaci and Sözbilir, 2006;Martin and Németh, 2007;Busby, et al, 2008;Haller and Németh, 2009;Nouri, et al, 2017); and to the most recent Pleistocene succession around 43,000-12,400 years ago (Mercurio, 2011). However, it has also been pointed out by (Skilling, et al, 2002) that in ancient deposits, it may be difficult to differentiate fragments obtained from this process from those of tectonic origin.…”