Stratigraphy and tectonic evolution of the Kazdağı Massif (NW Anatolia) based on field studies and radiometric ages

The Kazda Massif was previously considered as the metamorphic basement of the Sakarya Zone, a microcontinental fragment in NW Anatolia. Our new field mapping, geochemical investigations, and radiometric dating lead to a re-evaluation of previous suggested models of the massif. The Kazda metamorphic succession is subdivided into two major units separated by a pronounced unconformity. The lower unit (the Tozlu metaophiolite) is a typical oceanic crust assemblage consisting of ultramafic rocks and cumulate gabbros. It is unconformably overlain by a thick platform sequence of the upper group (the Sarkz unit). The basement ophiolites and overlying platform strata were subjected to a single stage of high-temperature metamorphism under progressive compression during the Alpine orogeny, accompanied by migmatitic metagranite emplacement. Radiometric age data obtained from the Kazda metamorphic succession reveal a wide range of ages. Metagranites of the Kazda metamorphic succession define a U-Pb discordia upper intercept age of ca. 230Ma and a lower intercept age of 24.8 +/- 4.6Ma. This younger age agrees with Pb-207/Pb-206 single-zircon evaporation ages of 28.2 +/- 4.1 to 26 +/- 5.6Ma. Moreover, a lower intercept age of 28 +/- 10Ma from a leucocratic metagranite supports the Alpine ages of the massif within error limits. Reconnaissance detrital zircon ages constrain a wide range of possible transport and deposition ages of the metasediments in the Sarkz unit from ca. 120 to 420Ma. Following high-temperature metamorphism and metagranite emplacement, the Kazda sequence was internally imbricated by Alpine compression, and the lowermost Tozlu ophiolite thrust southward onto the Sarkz unit. Field mapping, internal stratigraphy, and new radiometric age data show that the Sarkz unit is the metamorphic equivalent of the Mesozoic platform succession of the Sakarya Zone. The underlying metaophiolites are remnants of the Palaeo tethys Ocean, which closed during the early Alpine orogeny. After strong deformation attending nappe emplacement, the unmetamorphosed Miocene Evciler and Kavlaklar granites intruded the tectonic packages of the Kazda Massif. During Pleistocene time, the Kazda Massif was elevated by EW trending high-angle normal faults dipping to Edremit Gulf, and attained its present structural and topographic position. Tectonic imbrication, erosion and younger E-W-trending faulting were the main cause of the exhumation of the massif

Carboniferous granites on the northern margin of Gondwana, Anatolide-Tauride Block, Turkey – Evidence for southward subduction of Paleotethys

Carboniferous metagranites with U-Pb zircon crystallization ages of 331-315 Ma crop out in the Afyon zone in the northern margin of the Anatolide-Tauride Block, which is commonly regarded as part of Gondwana during the Late Palaeozoic. They are peraluminous, calc-alkaline and are characterized by increase in Rb and Ba, decrease in Nb-Ta, and enrichment in Sr and high LILE/HFSE ratios compatible with a continental arc setting. The metagranites intrude a metasedimentary sequence of phyllite, metaquartzite and marble; both the Carboniferous metagranites and metasedimentary rocks are overlain unconformably by Lower Triassic metaconglomerates, metavolcanics and Upper Triassic to Cretaceous recrystallized limestones. The low-grade metamorphism and deformation occurred at the Cretaceous-Tertiary boundary. There is no evidence for Carboniferous deformation and metamorphism in the region. Carboniferous arc-type granites and previously described Carboniferous subduction-accretion complexes on the northern margin of the Anatolide-Tauride Block suggest southward subduction of Paleotethys under Gondwana during the Carboniferous. Considering the Variscan-related arc granites in Pelagonian and Sakarya zones on the active southern margin of Laurasia, a dual subduction of Paleotethys can be envisaged between Early Carboniferous and Late Permian. However, the southward subduction was short-lived and by the Late Permian the Gondwana margin became passive. (C) 2016 Elsevier B.V. All rights reserved