Nappe Imbrication Within the Phyllite‐Quartzite Unit of West Crete: Implications for Sustained High‐Pressure Metamorphism in the Hellenide Subduction Orogen, Greece

Abstract

We report four K‐Ar fault‐gouge and eight U‐Pb calcite ages from the high‐pressure Phyllite‐Quartzite Unit (PQ) and the overlying, strongly thinned non‐high‐pressure Tripolitza and Pindos units of western Crete, Greece. We relate consistent 26–21 Ma fault‐gouge ages to a discrete top‐to‐the‐S, brittle‐ductile, contractional shear zone (Intra‐PQ Thrust) that formed during high‐pressure conditions within the Phyllite‐Quartzite Unit. The Intra‐PQ Thrust separates the Phyllite‐Quartzite Unit into an upper and a lower unit and is associated with gypsum deposits and high finite strain. Below the Intra‐PQ Thrust, U‐Pb calcite ages between about 16 and 13 Ma are also associated with top‐to‐the‐S kinematic indicators and, in part, developed during aragonite stability. The brittle‐ductile contact zone to the overlying Tripolitza and Pindos units yielded U‐Pb calcite ages of 13 to 12 Ma. Our data imply that the upper Phyllite‐Quartzite Unit underwent high‐pressure metamorphism at the commonly envisaged time of 24–21 Ma. However, the lower Phyllite‐Quartzite Unit started to be underthrust at 26–21 Ma and was high‐pressure metamorphosed at 16–13 Ma, as suggested by the U‐Pb calcite ages of aragonite‐bearing samples and published zircon fission track ages. We discuss a tectonic model of successive underthrusting, high‐pressure metamorphism and subsequent exhumation of both Phyllite‐Quartzite units in extrusion wedges until 12–11 Ma, after which Crete underwent crustal extension. Our work suggests that there might be more than one Cretan Detachment. It also has implications for sustained underthrusting and exhumation of continental crust in subduction zones.

Transition From Late‐Miocene Syn‐Orogenic Extension to Plio‐Pleistocene Corinth Rifting in the Southern Hellenides, Northern Peloponnese, Greece

“…In the southern Peloponnese, this second phase of exhumation occurred during the Middle to Late Miocene (Marsellos et al, 2010). Ring et al (2022) date a late extensional phase as younger than 12-11 Ma in Crete, and Grasemann et al (2019) have demonstrated that the PQ Unit in central Crete was exhumed above the brittleductile transition at 15 Ma. Its timing in the Northern Peloponnese is so far unconstrained, but is likely to have started later, during the Late Miocene (Athanassas et al, 2021).…”

“…The kinematics of the Cretan detachment and associated exhumation of the PQ Unit in the southern Peloponnese and Crete are a subject of debate, with a range of exhumation models proposed, including: (a) a cold metamorphic core complex (van Hinsbergen & Meulenkamp, 2006); (b) post‐accretion bivergent extension (Fassoulas, 1999); (c) syn‐accretion extension (Jolivet et al., 1994, Jolivet et al., 1996); and (d) wedge extrusion within a subduction channel (Grasemann et al., 2019; Jolivet, Trotet, et al., 2010; Ring & Yngwe, 2018; Ring et al., 2022). In the Northern Peloponnese, the wedge extrusion model explains the presence of both ductile top to ENE and WSW shear bands within the PQ Unit as well as the presence of a more co‐axial style of deformation within the core of the exhuming unit (Kotowski et al., 2022; Lamont et al., 2020; Ring et al., 2010).…”

“…The second stage of exhumation of the PQ Unit can be explained by underplating and duplexing at depth within the subduction prism (Figure 14) (Athanassas et al, 2021;Jolivet et al, 1994;Marsellos et al, 2010;Menant et al, 2019Menant et al, , 2021Ring et al, 2022). Antiformal stacking of mid-upper crustal imbricates of the Apulian margin triggers vertical tectonic uplift within the supra subduction prism (Jamieson & Beaumont, 1988, 1989Platt, 1986).…”

Cenozoic evolution of the Tripolitza carbonate platform in the Tethyan realm: new age constraints on deposition, diagenesis, metamorphism and nappe emplacement based on U-Pb and Rb-Sr dating (External Hellenides, Crete)

“…10–11 Ma, which are slightly younger than U-Pb calcite ages reported from the nappe contact between TPU/Pindos Unit and the lower nappes (12–13 Ma, Ring et al . 2022). The younger generation was formed between 7 and 9 Ma (Fig.…”

“…(1) K-Ar and 39 Ar- 40 Ar ages of white mica obtained from phyllites of the Phyllite-Quartzite Unit s.str. of central and western Crete range from 24 to 19 Ma regarded as the time of HP-LT metamorphism (Seidel et al 1982; Jolivet et al 1996; Ring et al 2022). (2) Fission-track ages of zircon yielded an arithmetic mean sample age at 18.6 ±1.9 Ma suggesting cooling below ca.…”