From Mesoproterozoic magmatism to collisional Cretaceous anatexis: Tectonomagmatic history of the Pelagonian Zone, Greece

Abstract

The magmatic history of the Pelagonian Zone, in northern Greece, is constrained with secondary ion mass spectrometer (SIMS) U-Pb dating on zircons of various granitoids whose structural positions were defined with respect to the regional main foliation. Ages pertain to four groups: (i) Mesoproterozoic (circa 1430 Ma) crystallization of granites inferred from inherited magmatic zircon cores that have been partially molten during the (ii) Neoproterozoic at circa 685 Ma (metamorphic zircon rims) and subsequently intruded by a Neoproterozoic leucogranite (circa 600 Ma). (iii) Late-or post-Variscan calc-alkaline granitoids (315-301 Ma) were in turn intruded by a subvolcanic dike at about 280 Ma. In the Early Permian the εNd(t) in magmas decreased from À7.3 to À1.3, hinting to mantle-derived melts produced during extension. Rifting is further heralded by two acidic and one mafic dike containing Lower-Middle Triassic zircons (246-242 Ma). (iv) Early Cretaceous anatectic melts at 117 ± 8 Ma formed during regional metamorphism. This age is the first report of in situ anatexis in the Pelagonian Zone. Cretaceous anatexis developed during the Mesozoic collision of Pelagonia with the Eurasian margin. Major-and trace-element geochemistry of amphibolites further attests for the complex pre-Alpine tectonic history with Neoproterozoic calc-alkaline and back-arc geochemical signature and Triassic alkali-magmatism.

Polyphase evolution of Pelagonia (northern Greece) revealed by geological and fission-track data

“…1a). After the Variscan orogeny and Permian-Triassic rifting, Pelagonia was part of a continental block bounded to the northeast by its passive margin (the AVAZ) and a seaway of the Tethys Ocean (e.g., Sharp and Robertson, 2006;Schenker et al, 2014). To the southwest, Pelagonia is delimited by the Pindos basin (e.g., Bernoulli and Laubscher, 1972).…”

“…The continental Precambrian basement of Pelagonia has been intruded by Carboniferous (late Variscan) and PermoTriassic (Tethys rifting) granitoids (Anders et al, 2007;Schenker et al, 2014); volcano-sedimentary rocks and carbonates are attributed to the cover of the crystalline rocks (e.g., Kilias et al, 2010). Carbonates, ultramafic rocks and metavolcanites of the AVAZ (schematically represented in Fig.…”

“…1) with main tectonic events. From southwest to northeast: tectonism of Paxos, Ionian, Gavrovo-Tripolitza and Pindos zones (typical localities of the first deposition of the synorogenic mass flow deposits) according to Papanikolaou (1997); Pelagonian unconformity and deformation according to Kilias et al (2010) and Schenker et al (2014), respectively; Paikon (Late Cretaceous/Early Tertiary window in the AVAZ) tectonism according to Bonneau et al (1994) and Mercier and Vergely (1994); deformation and transgressions of Serbo-Macedonia (the westernmost continental fragment of the Rhodope) and the Southern and Northern Rhodope Complexes (two extensional metamorphic core complexes) according to Burg (2012) and Ivanova et al (2015).…”

“…1a, Schermer et al, 1990;Kilias et al, 2010;Schenker et al, 2014) is tectonically overlain by imbricates of a Late Triassic-Middle Jurassic passive margin (the Axios/Vardar/Almopias zone, AVAZ) to the northeast (e.g., Bernoulli and Laubscher, 1972). Pelagonia and the AVAZ are exposed between two composite nappe complexes with distinct orogenic histories (Figs.…”

“…To the southwest, the fold-and-thrust belt of the External Hellenides formed during Eocene-to-Miocene times (e.g., Aubouin, 1973). The Pelagonian zone experienced two thrust events, one during the late Early Cretaceous and the next during the Eocene (Godfriaux et al, 1988;Schermer, 1993;Schenker et al, 2014) followed by Miocene extension (e.g., Schermer et al, 1990;Lecassin et al, 2007;Coutand et al, 2014). This history imprinted a complex distribution of low-temperature thermochronometric data, which comprise: zircon fission track (ZFT), zircon (U-Th) / He (ZHe), apatite fission track (AFT) and apatite (U-Th) / He (AHe) (Most, 2003;Vamvaka et al, 2010;Coutand et al, 2014).…”