First Record of Late Devonian Within-Plate Basic Magmatism in the Menderes Massif (Western Türkiye): Implications for Extension Along the Northern Margin of Gondwana

Abstract

The timing of the extensional event in the northern part of Gondwana remains unclear. To constrain this event, I present new zircon U-Pb age, Hf isotopic compositions, and whole-rock major-/trace-element and Sr-Nd isotope data for the metabasic rocks (amphibolite) in the basement unit of the Menderes Massif (MM) belonging to the Anatolide-Toride Block (ATB). Zircon LA-ICP-MS U-Pb dating of a sample yielded crystallization ages of 367.0±2.5 Ma, revealing the first record of the Late Devonian (Famennian) basic magmatism in the MM. This amphibolite contains a population of inherited zircon grains ranging from 588 Ma to 522 Ma, likely derived from the late Neoproterozoic country rocks. The whole-rock chemistry of the amphibolite suggests a basic derivation (e.g., SiO2 50 wt%; Al2O3 14 wt%; Ni 25-36 ppm). Chondrite-normalized rare earth elements (REE) patterns show enrichment in light rare earth elements (LREE) and flat heavy rare elements (HREE) patterns, suggesting affinities with the tholeiitic EMORB and ocean island basalt (OIB). They have weak to absent Eu anomalies. The Sr-Nd isotopic data show low 87Sr/86Sr(i) of 0.697317, εNd(i) = +0.7, and Nd-TDM = 1047 Ma. The geochemical characteristics, together with the positive eHf(t) values of 0.5–7.8, imply that amphibolite are most likely derived from the juvenile melts. The geochemical data suggest that the Late Devonian primary magma were derived from partial melting of asthenospheric mantle component, which were subsequently modified by crustal contamination and fractional crystallization. The contemporaneous EMORB- and OIB-like tholeiitic and alkaline basalt and amphibolite were also found in the eastern Taurides and in Iran. Both regional geological and geochemical constraints suggest that Late Devonian magmatism in the ATB occurred in a within-plate tectonic environment. It is envisaged that the northward subduction of the Paleotethys beneath the Pontides during the Devonian resulted in pull-forces and extensional tectonic regime on the northern margin of the Gondwana.

Keywords: Basic intrusion, Within-plate magmatism, Extension, Menderes Massif, Anatolides, Gondwana