U-Pb zircon and titanite ages and Sr-Nd-Hf isotope constraints on the timing and evolution of the Petrohan-Mezdreya pluton (Western Balkan Mts, Bulgaria)

Abstract

A combination of methods is applied in the present study to define the exact age of the Petrohan and Mezdreya plutons and trace their magma evolution. Field, petrological, and geochemical studies of the Petrohan pluton revealed its complex evolution and emphasized the role of magma mingling and mixing, complementary to the normal assimilation and fractional crystallization (AFC) processes. Using high-precision conventional U-Pb (CA)-ID-TIMS zircon and titanite dating in combination with CA-LA-ICP-MS zircon dating and tracing, we suggest an incremental growth of a common Petrohan-Mezdreya pluton. It was assembled over minimum 4.5 Ma from 311.14±0.48 Ma to 307.54±0.54 Ma. The younger age of the gabbro (308.12±0.33 Ma), compared with the age of granodiorites (311.14±0.48 Ma), provides numerical proofs for magma replenishment during the assembling of the Petrohan pluton. Whole-rock strontium-neodymium (initial 87Sr/86Sr ratios of 0.70521–0.70527 to 0.70462 and 143Nd/144Nd of 0.51221 to 0.51210) and Hf-zircon isotope data (ε-Hf from –5.8 to +3.6) argue for interaction of mantle derived magma with crustal melts but also mixing and mingling and transfer of zircon grains between the gabbroic and granitic melts. Possible petrogenetic scenario includes melting of subcontinental mantle lithosphere and crust and evolution trough AFC, FC and mingling/mixing processes. Considering the Petrohan-Mezdreya pluton as part of the Variscan orogeny in SE Europe, our new data support the accretion/collision of both the Balkan and Sredna Gora/Getic units with Moesia in the Early Carboniferous followed by syn- and post-collisional Carboniferous and Permian magmatism.