Multiphase magmatic activity in the Variscan Kłodzko-Złoty Stok intrusion, Polish Sudetes: evidence from SHRIMP U-Pb zircon ages

摘要

The Kodzko-Zoty Stok intrusion (KZSI), located in the NE part of the Bohemian Massif of Central Europe, has preserved records of the magmatic and tectonic activity of the Variscan orogeny in the Sudetes. KZSI is extraordinarily complex texturally, and shows a very wide range of chemical, isotopic and mineralogical compositions which indicates a complex, multiphase history of intrusion. New SHRIMP U-Pb zircon ages provide evidence of two magmatic episodes with a distinctive hiatus between them at similar to 326-308 Ma. The youngest dated zircons (303.8 +/- 3.8/4.2 Ma) are from the Laski leucocratic hornblende-biotite monzogranite and mark a short interval of post-collisional reactivation of the magma system. Zircons from a biotite-hornblende diorite sheet from the northern part of KZSI yielded an age of 349 +/- 3.4/3.7 Ma, interpreted as indicating the initial phase of an early Carboniferous, multi-pulse episode. The evolution of the magmatic system can be tied to a 334.4 +/- 2.9/3.3 Ma zircon age for melanocratic syenites from Podzamek which represent lamprophyric melt. Based on textural and compositional data and field relationships we interpret the intrusion as having been tilted post-emplacement towards the NW. This, together with the new dating results, ties the early Carboniferous episode of KZSI activity and the Jawornik granitoids (5 km to the SE) to the same magmatic system and arguably to bentonites of the Paprotnia beds (5 km to the NW), all representing different levels of such a system. The newly estimated late Carboniferous age from Laski ties part of the KZSI to other late Carboniferous Sudetic intrusions and late Carboniferous-Permian volcanism.