Different age response of zircon and monazite during the tectono-metamorphic evolution of a high grade paragneiss from the Ruhla Crystalline Complex, central Germany

Results of TIMS, SIMS and SEM analyses show that zircon and monazite in a high-grade paragneiss of the Ruhla Crystalline Complex, central Germany, were formed and/or altered during different stages of a tectono-metamorphic history between Early Devonian and Permian times. Detrital zircon cores of >460 Ma place an older limit on the age of anatexis, and show that the paragneiss sequence contains rocks at least as young as early Cambrian. Metamorphic zircon growth commenced at similar to365 Ma, peaking at similar to360-355 Ma at the same time that granite dykes were emplaced. In contrast, monazite in the paragneiss preserves little record of the metamorphic peak. Most monazite grains grew or were recrystallised in the Lower Carboniferous at similar to339 Ma, contemporaneous with the emplacement of voluminous diorite and granite bodies. These intrusions and related tectonics caused some of the high-U zircon overgrowths to undergo moderate to severe Pb loss. A second Pb loss event, between 300 and 280 Ma, can be related to Late Carboniferous/Early Permian large-scale block faulting.