Petrology and zircon U-Pb geochronology of mafic-intermediate dykes in the West-Central Taurides: Implications for magma source during the Late Precambrian - Early Palaeozoic

Abstract

Cadomian magmatic activity is represented by a mafic - intermediate dyke suits in the Karacahisar dome (West - Central Taurides) formed by the southward subduction of the Proto-Tethyan ocean beneath North Gondwana. These dyke suites are classified as diabase, andesite and dacite. They display calc-alkali, high-K calc-alkali and shoshonitic character, and intruded into the siliciclastic rocks deposited in a back-arc rift setting. In this study, we present new zircon U-Pb ages, Sr-Nd isotopic and geochemical data to better understand the petrological evolution of the Cadomian magmatism. Zircon U-Pb concordia ages of 551.3 +/- 3.5 Ma, 557.9 +/- 3.7 Ma and 569 +/- 7.2 Ma were obtained for these dykes. On the N-MORB normalized spider diagrams, mafic - intermediate dykes exhibit enrichment in large ion lithophile elements (LILE: Sr, K, Rb, Ba, Th), relatively less enrichment in light rare earth elements (LREE: La, Ce and Nd) and depletion in high field strength (HFS: Tb, Ti, Y and Yb) elements. Dyke samples have significant depletions of Ta and Nb relative to neighbouring LILE and LREE and display a significant subduction component. On the chondrite normalized REE diagrams, a weak Eu anomalies are observed, and this indicates some plagioclase accumulation. Dyke samples fall into the volcanic arc (island arc and/or continental arc), and back-arc fields on tectonic setting discrimination diagrams. The epsilon Nd-(i) values of dykes range from -1.47 to 1.76, and Nd depleted-mantle model (T-DM) ages vary between 1.32 and 1.81 Ga, and show enriched mantle or metasomatized subcontinental lithospheric mantle source signatures. The primary magmas of the dykes were derived from amphibole- and garnet-bearing mantle, and were affected by fractional crystallization, mixing and assimilation processes during ascent through the upper crust. All available data show that this magmatic activity developed in a back-arc rift setting subsequent to Cadomian arc magmatism in the West-Central Taurides.