Mineralogic evidences of a mid-Paleozoic tectono-thermal event in the Zonguldak terrane, northwest Turkey: implications for the dynamics of some Gondwana-derived terranes during the closure of the Rheic Ocean

Abstract

The Zonguldak terrane is a Gondwana-derived continental microplate along the Black Sea coast in northwest Anatolia. It includes a Cadomian basement, with oceanic- and island-arc sequences, unconformably overlain by siliciclastic rocks of Ordovician to Middle Silurian age. After a period of deformation and erosion, late Lower Devonian (Emsian) quartzites and shallow-marine limestones unconformably cover Middle Silurian (Wenlock) graptolitic shales. Along several cross sections across the unconformity plane, the mineralogical characteristics of the Paleozoic sedimentary rocks in the Zonguldak terrane are studied to check whether this regional unconformity is only of epeirogenic nature or the result of a thermal event. In addition to the appearance of kaolinite in Devonian units, crystal-chemical data of illites show a sudden jump at the unconformity plane. The b cell dimension values of illites of Ordovician–Silurian units are somewhat higher than those of Devonian–Carboniferous units and show a drastic drop between the Silurian and Devonian units. The new mineralogic data indicate that the pre-Emsian rocks in the Zonguldak terrane experienced a thermodynamo event, prior to the Emsian transgression. This Caledonian-time event is also reported in east Moesian terrane but not noticed in the neighboring Istanbul–Zonguldak and in the west Moesian – Balkan – Kreishte terranes. By this, it is suggested that Zonguldak and east Moesian terranes behaved independently from the Istanbul–Balkan terranes during the closure of the Rheic Ocean. They very likely docked to Laurussia during Emsian by strike-slip faults and remained thereon at its platform margin, where the Middle–Late Devonian shallow-platform conditions were followed by fluvial (lagoon and delta) conditions and deposition of coal during Late Carboniferous.

New Detrital Zircon Geochronology From the Cycladic Basement (Greece): Implications for the Paleozoic Accretion of Peri‐Gondwanan Terranes to Laurussia

“…The Early Devonian magmatism, thus, was triggered by accretion of an island arc to the Laurussian margin (Franke, ). Such tectonic settings may explain the differences between Zonguldak and Istanbul (sensustricto) terranes in the Pontides, where the Early Devonian tectonothermal event is recorded by Paleozoic sedimentary rocks of the Zonguldak, but not by the neighboring Istanbul terrane (Bozkaya et al, ).…”

Clay mineralogy, chemistry, and diagenesis of Late Devonian K-bentonite occurrences in northwestern Turkey

“…However, it may be suggested that these tephra layers were formed in relation with arc-volcanism, generated by the closure of the Variscan Rheic Ocean (Nzegge et al, 2006;Okay et al, 2010;Bozkaya et al, 2012).…”

“…The formation is overlain by a sequence of more than 500 m thick of alternating limestones and shales (Figures 1c and 2, Madendere and Karadon formations), followed by flood-plain deposits with numerous coal-stems of Westphalian age (Kerey, 1984). Bozkaya et al, 2012). (c) Geological map of the study area and geographic settings of sampling quarries (modified from Akbaş et al, 2002).…”

Ordovician graptolites from the basal part of the Palaeozoic transgressive sequence in the Karadere area, Zonguldak Terrane, NW Turkey; pp. 227–232

“…Ghienne et al 2010 and references therein), fossil data from the Lower and Middle Ordovician rocks are relatively scarce in the Istanbul and Zonguldak terranes of NW Anatolia (e.g. Yanev et al 2006;Bozkaya et al 2012). In the Eastern part of the Zonguldak Terrane, the Safranbolu-Karadere area (Fig.…”