The Jurassic meta-ophiolitic rocks of Cape Steno, Andros, Greece: a high-pressure/low-temperature melange with Pelagonian affinity in the Cycladic Blueschist Unit?

This study aims at clarifying the relationship between the Cape Steno melange, southern Andros, and the main tectonic units of the Attic-Cycladic Crystalline Belt. Jurassic protolith ages and geochemical characteristics indicate a Pelagonian affinity and point to a correlative relationship with the Tsiknias Ophiolite on Tinos Island. However, jadeitites and high-Si phengite in the gneisses clearly indicate a high-pressure metamorphic overprint that is unknown from the Tsiknias outcrop and other occurrences of the Upper Cycladic Unit. A correlation with the Cycladic Blueschist Unit (CBU) is an obvious assumption, but initially seemed difficult to reconcile with the Cretaceous protolith ages of meta-ophiolitic rocks from the CBU and distinct geochemical characteristics of associated jadeitites. The Jurassic ages of the Cape Steno rock suite either document a broader spectrum of source rocks than previously known from the CBU, or the existence of a distinct tectonic unit. We assume that the geological and tectono-metamorphic evolution of the Cape Steno occurrence is similar to that of the Makrotantalon Unit of NW Andros, which represents a Pelagonian subunit in the nappe stack of the CBU, with abundant slices of serpentinites, rare meta-gabbro and a metamorphic history comprising both Cretaceous and Eocene HP/LT episodes.

Automated summary

This study aims to clarify the relationship between the Cape Steno melange in southern Andros and the main tectonic units of the Attic-Cycladic Crystalline Belt. The results suggest a Pelagonian affinity and the presence of a high-pressure metamorphic overprint. This study provides new insights into the geological and tectono-metamorphic evolution of the Cape Steno occurrence.