Fission‐track thermochronology, vertical kinematics, and tectonic development along the western extension of the North Anatolian Fault zone

Abstract

We have investigated the low‐temperature history of pre‐Neogene basement areas adjacent to the western extension of the North Anatolian Fault zone (NAFZ) by apatite fission track thermochronology of 33 samples taken from Marmara island, Kapidag peninsula (both in the Sea of Marmara), Samothrake island, and Chalkidike peninsula (both in the North Aegean region). Together with already published apatite fission track data from 30 other sampling localities of the region, these data (63 in total) have been evaluated mainly with regard to the transitional period from the Mesohellenic orogeny (Eocene‐Oligocene) to the plate‐tectonical individualization of the Aegean‐Antolian microplate, to gain a better understanding of the tectonical chronology that has led to modern east Mediterranean plate tectonics. Apatite fission track investigations of the area under discussion reveal two major events of cooling and exhumation of pre‐Neogene rocks. A first frequency maximum of cooling ages between 35 and 25 Ma (late Eocene to early Oligocene) is due to postorogenic regional erosion after the climax of the Mesohellenic orogeny, which was caused by continental collision of the Pelagonian platform and the Rila‐Rhodope zone after the final closure of the Axios‐Vardar Ocean. A second frequency maximum of cooling ages between 17 and 11.5 Ma (early to middle Miocene) depicts more localized uplift and exhumation in consequence of transpressive and/or transtensive movements along early structural discontinuities that gave rise to the later fault systems in the western extension of the NAFZ. The earliest fault structures of this system have developed shortly after the orogenic collapse and crustal extension of the Rila‐Rhodope area but quasi simultaneously with the onset of subduction along the modern Hellenic trench. The regional distribution of fission track ages of the Miocene age group (17 to 11.5 Ma), and corresponding thermochronological calculations based on frequency distributions of confined track lengths suggest that an early fault propagation has occurred from east to west during the Miocene. The onset of subduction along the Hellenic trench and subsequent gravitational retreat of the subducting oceanic slab are considered as a major cause for transtension of the Aegean crust, especially with regard to the development of north Aegean pull‐apart basins. Such early fault structures have facilitated the westward propagation of a continuous NAFZ that took place during the Pliocene from the easternmost Marmara region to the Gallipoli peninsula and to the North Aegean trough.

Upper Cretaceous exhumation of the western Rhodope Metamorphic Province (Chalkidiki Peninsula, northern Greece)

“…Using the same modeling approach and the samples GR117, GR126, GR132, and GR134 from Hejl et al . [], we calculated, for comparison, the thermal path of the lower Eocene Sithonia pluton from the southern edge of the Chalkidiki peninsula (see Figure for location). (bottom) The corresponding FT age (blue), mean track length (red), and kinetic parameter (green) predictions for the constrained and nonconstrained models are shown.…”

“…The cooling path crosses the high‐temperature limit of the apatite FT partial annealing zone (~120°C) at uppermost Cretaceous (between 62 and 70 Ma) and remains at temperature <50°C since the lower Eocene. Using the available geochronology data [ Hejl et al ., ] for a typical Lower Eocene pluton of the first magmatic pulse (Sithonia pluton from the southern tip of the Chalkidiki peninsula; Figure ) and the profile modeling technique described in a previous section, we can demonstrate that this pluton cooled to 50°C as early as lowermost Oligocene (~33 Ma), i.e., 10–15 Myr later than the surrounding basement rocks (Figure ). Thus, it can be concluded that none of the two magmatic pulses penetrating the Vertiskos Unit (Eocene and Oligo‐Miocene) were strong enough to cause regional thermal perturbations.…”

“…The Rhodope Metamorphic Province is made of three main tectonic domains that display first‐order similarities and differences in terms of cooling to near‐surface temperature (Figure ). The available low‐temperature thermochronology data [from Bigazzi et al ., ; Kyriakopoulos et al ., ; Hejl et al ., , ; Magganas et al ., ; Wuthrich , ; Kounov et al ., ; Márton et al ., , and the results of this study] are summarized in the histograms of Figure . For the NRC low‐temperature data are from both the migmatitic gneiss domes and their peripheries.…”

The Early Eocene Ekmekçi granodiorite porphyry in the Karacabey region(Sakarya Zone, NW Turkey)

“…Furthermore, there are Eocene plutonic rocks of various shapes and sizes intruding into the pre-Paleocene units of the eastern Pontides, Sakarya, and Tavşanlı Zones in NW Anatolia (Harris et al, 1994;Köprübaşı and Aldanmaz., 2004;Topuz et al, 2005Topuz et al, , 2011Karacık et al, 2008;Ustaömer et al, 2009;Karslı et al, 2011;Altunkaynak et al, 2012;Ersoy and Palmer, 2013;Topuz and Okay, 2017). During Oligocene time a regional exhumation took place (Hejl et al, 2010;Cavazza et al, 2012) and the whole of the Pontides, except the westernmost part (northern and eastern part of the Thrace basin; Less et al, 2011;Okay et al 2019), was uplifted above sea level. Thus, the Eocene sediments represent the last marine deposits in most of the Pontides.…”

Thermochronological dating of brittle structures in basement rocks: A case study from the onshore passive margin of SW Sri Lanka

“…Here, the thermal sensitivity of (U‐Th‐Sm)/He and apatite FT systems to low‐temperatures between 40°–80°C and ∼60°–120° [e.g., Green et al , 1986; Farley , 2000] provides a unique perspective for fault dating. Most apatite based thermochronological estimate studies estimate fault ages indirectly by comparing the cooling histories of the foot and hanging wall sections across major faults [e.g., Ehlers and Farley , 2003; Redfield et al , 2005; Seiler et al , 2010; Hejl et al , 2010]. Past attempts to directly date heat transfer along faults by apatite FT and (U‐Th‐Sm)/He data were usually less successful.…”