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

Abstract

Abstract 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 a formerly presented age of 298 ±2 Ma. 207Pb/ 206Pb 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.