Implications of U–Pb and Lu–Hf isotopic analysis of detrital zircons for the depositional age, provenance and tectonic setting of the Permian–Triassic Palaeotethyan Karakaya Complex, NW Turkey

Abstract

New zircon U–Pb age data, combined with Lu–Hf isotopic data, are presented here for sandstones of mainly arkosic composition from the Permian–Triassic Karakaya Complex. Predominantly, Carboniferous, Triassic and Devonian zircon age groups are recognised, most of which have a Late Triassic (Carnian–Norian) maximum depositional age. Carboniferous- and Devonian-aged zircon populations exhibit intermediate e Hf(t) values (−11 to +2), consistent with formation in a continental margin arc setting where juvenile mantle-derived magma mixed with (recycled) old crust of Palaeoproterozoic Hf model age. In contrast, the Triassic-aged zircon population exhibits higher e Hf(t) values (−5 to +4), consistent with mixing of juvenile mantle-derived melts with (recycled) old crust of Neoproterozoic Hf model age. Potential igneous source rocks for the sandstones of the Karakaya Complex exist in the Devonian and Carboniferous granitic rocks of the Sakarya continental basement to the north. Their e Hf(t) and corresponding model ages are nearly identical to the age-equivalent zircon populations within the Karakaya Complex sandstones. However, the Triassic granitic rocks of the Sakarya continental crust differ significantly in e Hf(t) and corresponding model age from the sandstones of the Karakaya Complex. Late Triassic sandstones from the Tauride continental unit to the south lack the dominant Late Palaeozoic and Triassic zircon populations of the Karakaya Complex sandstones. Triassic granitic bodies and intermediate-composition extrusive rocks in the Tauride continental unit also differ in e Hf(t) and corresponding Hf model ages from the Karakaya Complex sandstones. In addition, Late Triassic sandstones of the Kocaeli Triassic unit (Istanbul Terrane) in the north differ strongly from the Karakaya Complex sandstones in zircon population ages and e Hf(t). In the regional context, the new zircon age and lutetium–hafnium isotopic data are consistent with derivation of the Late Triassic Karakaya Complex sandstones from a Late Palaeozoic–Triassic continental margin arc located somewhere along the southern margin of Eurasia, although its exact position cannot be pinpointed at present owing to lack of suitable outcrop and comparable isotopic data.