Michael Walsh

The NW Aegean is a long-studied region experiencing Tertiary N-S extension in the rear of the South Hellenic Subduction Zone (Fig. 1) (Gautier et al., 1999).  There is some consensus that Aegean extension is the result of a southward migration of the Hellenic arc from rollback of the subducting slab (Berckhemer, 1977; e.g. Jolivet and Brun, 2010).  The migration of this subduction zone creates a free boundary allowing the Aegean crust, previously thickened from Early Tertiary alpine collision, to gravitationally spread in a southward direction (e.g. Gauthier et al., 1999, Lacassin et al., 2007; Nance, 2010).  Also impacting this region is the westward escape of Anatolia along the North Anatolian Fault (NAF) caused by the Middle to Upper Miocene collision of Arabia and Eurasia (e.g. Gautier et al., 1999, Lacassin et al., 2007) (Fig. 1).  Recent studies suggest kinematic and mechanical interactions between Aegean extension and displacement along the right-lateral strike-slip North Anatolian Fault.  The NAF propagated westward into the northern Aegean domain about 5 Ma ago, and is thought to have initiated a rapid phase of crustal cooling and exhumation at that time.  (Lacassin et al., 2007, Flerit et al., 2004).

            The Olympus-Ossa massif is located in the northwestern part of the Aegean domain, in the footwall of an active normal fault, and at the westward extent of the North Anatolian Fault and is an ideal site to test the influence of the NAF on Neogene crustal cooling (Fig. 1).  The core of the modern Olympus-Ossa tectonic windows have been exhumed through divergent low-angle extensional shear zones (Killias et al., 2002) followed by high-angle normal faulting during the latest Tertiary-Quaternary (Schermer, 1993; Lacassin et al., 2007; Nance, 2010) at timing and rates that remain poorly constrained.

            To test the hypothesis of the proposed post-5Ma rapid cooling event, I investigated  the Late Tertiary-Quaternary upper crustal cooling history of the Olympus-Ossa massif using apatite and zircon (U-Th)/He thermochronology on bedrock samples distributed in the tectonic windows and outside of them, across the Pelagonian domain.  (U-Th)/He ages were combined with unpublished apatite fission-track data and used in the inverse thermal modeling software HeFTy (Ketcham, 2005) to provide constraints on the low-temperature cooling history of the region.  The results show that a rapid cooling event occurred in the Olympus and Ossa massifs ~14-10 Ma ago, that lasted until ~9-5 Ma, suggesting that increased extension along the normal fault occurred prior to NAF propagation into the region, or that post-5 Ma cooling related to the NAF is not exposed in the modern landscape yet.

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Pages: 74
Supervisor: Isabelle Coutand