Preprints
https://doi.org/10.5194/se-2020-186
https://doi.org/10.5194/se-2020-186

  25 Nov 2020

25 Nov 2020

Review status: a revised version of this preprint was accepted for the journal SE and is expected to appear here in due course.

Evidence for the Late Cretaceous Asteroussia event in the Gondwanan Ios basement terranes

Sonia Yeung1, Marnie Forster1, Emmanuel Skourtsos2, and Gordon Lister1 Sonia Yeung et al.
  • 1Structure Tectonics Team, Research School of Earth Sciences, Australian National University, Canberra, 2601 Australia
  • 2Section of Dynamic, Tectonic and Applied Geology, Department of Geology and Geoenvironment, National and Kapodistrian University of Athens, Athens 157 72, Greece

Abstract. 40Ar/39Ar geochronology on garnet-mica schists and the underlying Gondwanan granitoid basement terrane on Ios demonstrates evidence of a Late Cretaceous high pressure, medium temperature (HP–MP) metamorphic event. This suggests that the Asteroussia crystalline nappe on Crete may extend northward and include Ios, in the Cyclades. If this is correct, the northern part of the Asteroussia nappe (on Ios) is overlain by the terrane stack defined by the individual slices of the Cycladic Eclogite-Blueschist Unit, whereas in the south (in Crete) the Asteroussia nappe is at the top of a nappe stack defined by the individual tectonic units of the external Hellenides. This geometry implies that the accretion of the Ios basement terrane involved a significant leap (250–300 km) southwards of the surface outcrop of the subduction megathrust. This accretion would have commenced at or about ~38 Ma, when the already exhumed terranes of the Cycladic Eclogite-Blueschist Unit had begun to thrust over the Ios basement. By ~35 Ma, we suggest the subduction jump had been accomplished, and renewed rollback began the extreme extension that led to the exhumation of the Ios metamorphic core complex.

Sonia Yeung et al.

 
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Sonia Yeung et al.

Sonia Yeung et al.

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Short summary
We do not know when the ancient Tethys Ocean lithosphere began to founder, but one clue can be found in subduction accreted tectonic slices, including Gondwanan basement terranes on the island of Ios, Cyclades, Greece. We propose a 250-300km southwards jump of the subduction megathrust, with a period of flat-slab subduction followed by slab break-off. The initiation and its subsequent rollback of a new subduction zone would explain the onset of Oligo-Miocene extension and accompanying magmatism.