Timing of Late Carboniferous/Permian Granite and Granite Porphyry Intrusions in the Ruhla Crystalline Complex (Central Germany), New Constraints from SHRIMP and ~(207)Pb/~(206)Pb Single Zircon Dating

摘要

The Ruhla Crystalline Complex (RCC) forms part of the NW trending Thuringian Forest horst block, which was affected by complex block faulting during Late Carboniferous/Early Permian times accompanied by an extensive magmatism. Block faulting results from dextral transtensive movements along the NW trending Franconian fault system, which separates the Saxo-Bohemian massif to the north from the South German block to the south. In the RCC granite bodies and a few magmatic dykes intruded along NE trending structures, whereas the majority of the magmatic dykes trend W, NW and ENE. SHRIMP zircon dating of the NE trending Trusetal Granite yielded a weighted mean age of 301(+-)5 Ma, identical to formerly presented age of 298(+-)2 Ma. ~(207)Pb/~(206)Pb single zircon evaporation dating of a ductily deformed NE trending granite porphyry dyke yielded an age of 294(+-)4 Ma, which is significantly older than an age of 285(+-)5 Ma obtained from a WNW-trending felsite porphyry dyke. Zircon xenocrysts in the felsite porphyry gave ages of 325(+-)9, 338(+-)4 and 543(+-)4 Ma, which indicate that crustal rocks were assimilated during magma generation and/or ascent. The presented geochronological data provide evidence that emplacement of granites and porphyry dykes along NE trending structures occured contemporaneously between 301 and 294 Ma, whereas magmatism along W to NW trending structures took place at about 285 Ma.