Structural and geochemical data of the Mourne nappe near Kerames (Crete): Constraints on the tectonometamorphic evolution of the Uppermost Unit

The Uppermost Unit of Crete is attributed to the Internal Hellenides and consists of different nappes derived from an Upper Cretaceous arc (Asterrousia), and a late Jurassic to Cretaceous subduction-accretion complex (Vatos, Arvi, Miamoux).  

Blueschists of the subduction-accretion complex of central Crete (Preveli nappe, T = ca. 350°C, P= ca. 1.2 GPa) are resting on top of Pindos rocks and are overlain by Cretaceous Vatos flysch, Jurassic ophiolites and a second sequence of blueschist-facies rocks referred to as Mourne nappe.

The Mourne blueschists show a large variety of amphiboles, such as glaucophane, riebeckite, richterite, ferri-winchite, barroisite, magnesio-hornblende, edenite and actinolite. K-Ar dating of barroisite and phengite yielded late Jurassic ages (Seidel et al., 1977).

Top-to-the SW shearing under epidote blueschist-facies conditions led to the dominant foliation of the Mourne metabasites, which is characterized by the shape-preferred orientation of blue amphibole, omphacite (as relics), epidote, rutile and titanite.

Growth of barroisite, magnesio-hornblende and epidote indicate isothermal decompression under epidote-amphibolite facies conditions.

Cooling and further decompression is indicated by several generations of younger veins mineralized with albite, quartz, epidote, actinolite (greenschist facies) and actinolite, epidote, prehnite, calcite (prehnite-actinolite facies).

The youngest deformation led to discrete foliation-parallel shear zones under brittle conditions, related to the emplacement of the Mourne nappe on top of the ophiolites.

Funding by DFG (Zu 73-34) is gratefully acknowledged.

References

Seidel E et al (1977) Metamorphic rocks of late Jurassic age as components of the ophiolitic mélange on Gavdos and Crete (Greece). Geol. Jb. 28:3–21