Geological characteristics and tectonic setting of the Kiruna-type magnetite-apatite ores in the Bitlis Massif (SE Anatolia, Türkiye)

Abstract

A complete section of the Bitlis Massif crops out in the Avnik and Ünaldı regions (E Türkiye). It comprises a core of Precambrian-Early Cambrian gneisses, mafic metavolcanic rocks with Kiruna-type magnetite-apatite ores and metagranite bodies. Unconformably overlying this core is a cover succession made up of Silurian to late Cretaceous micaschists and marbles. The Kiruna-type ore beds, focused on this paper, range from centimetres up to 20 m in thickness and are concordantly interbedded with mafic metalavas, detrital magnetite-rich metavolcanoclastic rocks, and metachert beds. Geological characteristics of the metamorphosed ore-bearing volcanic and volcanosedimentary succession indicate that the magnetite-apatite ores were formed in a shallow marine environment by volcanic exhalative and sedimentary processes. U-Pb zircon ages obtained from the interlayered basaltic flows are 578–542 Ma, marking the maximum age of ore formation. Geological and petrological characteristics of the basaltic association in the Precambrian units indicate that their formation took place in a forearc environment along the northern margin of Gondwana. This active magmatic margin was formed above the south dipping Prototethys oceanic crust, which was carrying a small oceanic or continental fragment. When this microcontinent collided with Gondwana, south-verging compressional deformation, high-grade regional metamorphism, and syntectonic intrusion of the Avnik and Yayla metagranites occurred. U-Pb zircon ages of 521–506 and 521–503 Ma for the Avnik and Yayla metagranites, respectively, date this collision, and thus the termination of ore deposition in the Bitlis Massif.