EARLY MESOZOIC OCEANIC SUBDUCTION-RELATED VOLCANIC-ROCKS, PINDOS BASIN, GREECE

Small outcrops of volcanic rocks of mid-Triassic to Early Jurassic age in the deep-water Mesozoic Pindos Basin have been systematically sampled and analysed geochemically to interpret the tectonic environment in which these rocks formed. Associated sediments indicate a rifting environment. The volcanic rocks include all the main types found in modern back-arc basins. Shoshonites with clinopyroxenes of calc-alkaline affinity occur at the basin margin. Minor enriched-type MORB contains clinopyroxene typical of MORB. Minor basalts that resemble OIB with some subduction-related characteristics contain clinopyroxene typical of alkaline rocks. Thick andesites and pyroclastic rocks with MORB-like trace elements, except for some LILE enrichment, are associated with cumulate gabbro and oceanic-type plagiogranite. These thick andesites and pyroclastic rocks formed at an intra-backarc ocean-ocean subduction zone. The supra-subduction zone ophiolites of the eastern margin of the Pindos Basin, which are of similar age, are probably related to the same subduction zone. The overall volcanic assemblage is related to formation of a back-arc basin associated with the subduction of Paleo-Tethys. The hypothesis that Late Triassic-Early Jurassic rifting formed only small pull-apart basins by transtension is inconsistent with the range of volcanic products and the evidence for significant intra-back-arc subduction.