Geochemical and Sr-Nd isotopic evidence for petrogenesis and geodynamic setting of Lower-Middle Triassic volcanogenic rocks from central Greece: Implications for the Neotethyan Pindos ocean

Abstract

Geochemistry and Sr-Nd isotopes were determined in Triassic calcalkaline metalava and metapyroclastic rocks from Attica and Argolida, central Greece, to ascertain their origin, evolution, and emplacement timing. Sample protoliths were lavas, tuffs, and, subordinately, tuffites of basaltic to rhyolitic composition. Despite up to low-grade hydrothermal metamorphism, samples retain primary structures and geochemical characteristics; in particular, relatively high (La/Lu) chondrite-normalized ratios, pronounced negative Eu anomalies, and Large Ion Lithophile Element (LILE) enrichment. Unlike the narrow Nd isotopic range (0.512342-0.512625), the Sr isotopic range is relatively wide (0.705903-0.711739). As Sr and Nd isotopic ratios do not provide concordant geochronological age for rock emplacement, they were corrected at 170 Ma due to geologic and petrographic considerations. Geochemistry and Sr and Nd isotopic ratios provide evidence of subduction metasomatism and crustal contamination affecting the parental magmas of samples. Their Nd model ages resemble those of Enriched Mid-Ocean Ridge Basalts (E–MORB) under the northern Aegean and Triassic-rift mafic rocks from northern Greece. As a whole, the geological and petrological data suggest that samples were formed both onshore and offshore in the transition zone between the Pelagonian microcontinent, moving away from Gondwana’s Apulian promontory, and the newly-formed intracontinental basin of the Neotethyan Pindos Ocean. A short-lived immature subduction of young oceanic crust under Pelagonia gave samples their strong geochemical and geological characteristics of volcanic-arc.