Investigation of petrology, geochronology and U-Th abundance of the western part of (North of Süloğlu) of Istranca Massif

The Istranca Massif is one of the prominent metamorphic massifs in Turkey. It comprises metasedimentary, metamagmatic, and metacarbonate rocks such as migmatite, ortho- and paragneiss, metagranite, metadiorite, garnet mica schist, calc-schist, and marble. This study focuses on identifying geochemically potential mineralization zones and source rocks for uranium-thorium (U-Th) enrichment and mineralization in the metamorphic basement units and the plutons of varying ages that intrude these units in the western part of the Istranca Massif. For the first time, the mineral chemistry of garnet mica schists in the northern-northwestern part of the massif has been analyzed to better understand the degree of metamorphism and to define the possible P-T (pressure-temperature) conditions. Zircon grains obtained from the orthogneisses in the study area yielded a U-Pb concordia protolith age of 302.33 ± 1.79 Ma. Additionally, detrital zircon U-Pb age dating was conducted on the garnet mica schists to determine their maximum depositional age. The youngest detrital zircon yielded a 206Pb/238U age of 198 ± 17 Ma, whereas the oldest zircon provided a 206Pb/238U age of 1896.8 ± 33.4 Ma. In-situ U-Pb age dating on rutile inclusions within almandine garnet grains in the garnet mica schists indicated that the rocks underwent metamorphism approximately 119 ± 49 Ma ago. By evaluating the mineral chemistry of almandine garnet and Fe-biotite, it was determined that the garnet mica schists experienced metamorphism under conditions of approximately 547°C and 6.1 kbar. These P-T conditions and the metamorphic age indicate that the rocks were affected by lower amphibolite facies metamorphism during the Late Jurassic to Early Cretaceous period. To evaluate the U-Th potential of the rocks, various lithologies and mineral assemblages were analyzed. The findings reveal that the studied rocks exhibit a certain potential for uranium and thorium enrichment. However, the geochemical and geological conditions required for the crystallization or accumulation of U-Th minerals were found to be insufficient. While the rocks have the characteristics of source rocks for uranium and thorium, the concentrations of these elements were not sufficient to form distinct U-Th minerals. Instead, uranium and thorium predominantly reside within accessory mineral phases. This study highlights the complexity of U-Th enrichment processes and provides insights into the metamorphic history and geochemical characteristics of the Istranca Massif.