The Late Cretaceous magmatic arc of the south Aegean: Geodynamic implications from petrological and geochemical studies of granitoids from Anafi island (Cyclades – Greece)

ABSTRACT

In the Aegean region (Cyclades – Greece), a large part of the Island of Anafi consists of exhumed high-grade metamorphic sequences (amphibolites, serpentinites and metasediments) that have been intruded by Late Cretaceous intermediate and felsic granitoids. These correspond to I-type arc-related rocks, displaying calc-alkaline geochemical affinities. Variability in their petrographic features, mineral composition and geochemistry is assigned to differentiation processes that mostly involved plagioclase and/or K-feldspar, and to a lesser extent amphibole and biotite. Mineral chemistry and geochemical results suggest that the Anafi granitoids are highly comparable with the Late Cretaceous granitoid intrusive rocks from East Crete and Donousa island.

The amphibole and zircon saturation thermometry yields relatively moderate temperature crystallization conditions (~790°C) for the intermediate granitoids and lower for the felsic granitoids (~630°C). Geobarometric calculations based upon the chemistry of magnesiohornblende, as well as the normative (Qz), (Ab) and (Or) contents clearly point to shallow intrusion conditions (~2.0–6.5 kbar), corresponding to an estimated depth of crystallization of ~12 ± 4 km. The thrust sheets that overly the Palaeogene flysch in Anafi (metasediments with serpentinized peridotites, amphibolites and metabasites), constitute a subducted and metamorphosed oceanic sequence. These metamorphic units likely represent a part of the Pindos – Cycladic Blueschist Unit domain that was subducted at an earlier pre-Campanian stage. In the hydrated mantle wedge, incorporation of shallow level granitoids within metamorphic units was likely facilitated via corner flow intrusion mechanisms. Following the intrusion, the granitoid rocks were exhumed in a syn-convergent setting, along with the metamorphic thrust sheets, by continuous underplating of more external units, thus, escaping penetrative ductile deformation.

KEYWORDS:

• Anafi
• granitoids
• metamorphic units
• exhumation
• corner flow

Acknowledgments

We would like to express our sincerest thanks to the Editor in Chief Dr. Robert J. Stern, as well as to two anonymous reviewers for their constructive reviews, suggestions, and critical comments, which significantly helped improve this paper. Franz Kiraly (University of Vienna) is gratefully acknowledged for assisting with the use of the electron microprobe facility.

Disclosure statement

No potential conflict of interest was reported by the authors.

Highlights

1. The Anafi Late Cretaceous granitoids correspond to I-type arc-related rocks, displaying calc-alkaline geochemical affinities.

2. Thermobarometric calculations yield relatively moderate temperature crystallization conditions (~790°C and ~630°C for the intermediate and felsic granitoids respectively) at shallow levels (~2.0-6.5 kbar at ~12 ± 4 km).

3. Incorporation of shallow level granitoids within the metamorphic units was likely facilitated via corner flow intrusion mechanisms.

4. The magmatic arc can be placed beneath the southern margin of the Pelagonian domain.

5. The metamorphic thrust sheets were exhumed in a syn-convergent setting.

Supplementary material

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