No significant Alpine tectonic overprint on the Cimmerian Strandja Massif (SE Bulgaria and NW Turkey)

Abstract

We provide the first comprehensive picture of the thermochronometric evolution of the Cimmerian Strandja metamorphic massif of SE Bulgaria and NW Turkey, concluding that the bulk of the massif has escaped significant Alpine-age deformation. Following Late Jurassic heat-ing, the central part of the massif underwent a Kimmeridgian-Berriasian phase of relatively rapid cooling followed by very slow cooling in Cretaceous-to-Early Eocene times. These results are consistent with a Late Jurassic-Early Cretaceous Neocimmerian (palaeo-Alpine) phase of north-verging thrust imbrication and regional metamorphism, followed by slow cooling/exhumation driven by erosion. From a thermochronometric viewpoint, the bulk of the Cimmerian Strandja orogen was largely unaffected by the compressional stress related to the closure of the Vardar-İzmir-Ankara oceanic domain(s) to the south, contrary to the adjacent Rhodopes. Evidence of Alpine-age deformation is recorded only in the northern sector of the Strandja massif, where both basement and sedimentary rocks underwent cooling/exhumation associated with an important phase of shortening of the East Balkan fold-and-thrust belt starting in the Middle-Late Eocene. Such shortening focused in the former Srednogorie rift zone because this area had been rheolo-gically weakened by Late Cretaceous extension.

The phanerozoic palaeotectonics of Turkey. Part I: an inventory

“…Only the evidence of the Cirligati Anticline in Romania and the isotopic ages of the muscovites in the Strandja Mountains show that the main Cimmeride deformations probably ended already sometime during the Jurassic, most likely during the Bajocian-Bathonian interval judging from the continuation of the Strandja zone to the east described below. The statement by Cattò et al (2018) that there is no significant Alpide overprint over the Cimmeride deformations cannot be taken seriously in view of the major Cretaceous arc magmatism that affected it and the thrusting of the entire massif over what seems to be an ophiolitic substratum in the south (see below).…”

Biostratigraphy and paleoenvironments of the Oligocene succession(İhsaniye Formation) at Karaburun (NW Turkey)

“…The inception and development of the Thrace Basin (Figure 8), a siliciclastic-dominated basin with more than 9 km of sediments within its central part, occurred during the Eocene (Turgut et al, 1991;Görür and Okay, 1996;Siyako and Huvaz, 2007). During the Eocene and Oligocene, the Strandja Massif formed a wide lowrelief ridge separating the two basins, as reflected in Late Cretaceous apatite fission-track ages (Cattò et al, 2017). Therefore, although close to the Thrace Basin, the geology of much of the Karaburun succession is quite distinct from the age-equivalent successions deposited in the Thrace Basin (Okay et al, 2019); in general, it has a more open marine character.…”

Eocene-Oligocene succession at Kıyıköy (Midye) on the Black Sea coast in Thrace

“…The Strandja Massif constitutes most of the basement to the Thrace basin. The Strandja Massif was deformed and metamorphosed during the latest Jurassic to earliest Cretaceous (Okay et al, 2001;Sunal et al, 2011), exhumed in the Late Cretaceous (Cattò et al, 2018) Cenomanian sandy limestones and passes up into a volcaniclastic-volcanic series, which constitutes part of the Late Cretaceous Pontide-Sredna-Gora magmatic arc (Okay et al, 2001). After the Early Eocene, the Strandja Massif formed a palaeogeographic high separating the Black Sea from the Thrace Basin ( Figure 2).…”