Early Variscan magmatism along the southern margin of Laurasia: geochemical and geochronological evidence from the Biga Peninsula, NW Turkey
Massive, fine-grained metavolcanic rocks of the Çamlıca metamorphic unit exposed in the Biga Peninsula, northwestern Anatolia, have provided new Carboniferous ages and arc-related calc-alkaline petrogenesis constraints, suggesting that the Biga Peninsula was possibly involved in the Variscan orogeny. The metavolcanic rocks are mainly composed of metalava and metatuff and have the composition of andesite. Chondrite-normalized REE patterns from these rocks are fractionated (LaN/YbN ~ 2.2 to 8.9). Europium anomalies are slightly variable (Eu/Eu* = 0.6 to 0.7) and generally negative (average Eu/Eu* = 0.68). The metavolcanic rocks have a distinct negative Nb anomaly and negative Sr, Hf, Ba, and Zr anomalies. These large negative anomalies indicate crustal involvement in their derivation. Tectonic discrimination diagrams show that all metavolcanic rocks formed within a volcanic arc setting. Zircon ages (LA-ICP-MS) of two samples yield 333.5 ± 2.7 and 334.0 ± 4.8 Ma. These ages are interpreted to be the time of protolith crystallization. This volcanic episode in the Biga Peninsula correlates with other Variscan age and style of magmatism and, by association with a collisional event leading to the amalgamation of tectonic units during the Variscan contractional orogenic event. Carboniferous calc-alkaline magmatism in the Sakarya Zone is ascribed to arc-magmatism as a result of northward subduction of Paleo-Tethys under the Laurasian margin. Geochemical and U–Pb zircon data indicate that the Sakarya Zone is strikingly similar to that of the Armorican terranes in central Europe. The Biga Peninsula shows a connection between the Sakarya Zone and the Armorican terranes.