Dating multiply overprinted granites: The effect of protracted magmatism and fluid flow on dating systems (zircon U-Pb: SHRIMP/SIMS, LA-ICP-MS, CA-ID-TIMS; and Rb-Sr, Ar-Ar) - Granites from the Western Erzgebirge (Bohemian Massif, Germany)

摘要

The Variscan granites from the Western Erzgebirge were repeatedly dated by various methods, but no consensus has been reached about their exact intrusion ages. This study presents a multi-dating approach for the four largest intrusions from the Western Erzgebirge (Aue-Schwarzenberg, Bergen, Eibenstock, Kirchberg). We analysed several samples from each pluton/suite with zircon U-Pb CA-ID-TIMS (chemical abrasion-isotope dilution-thermal ionization mass spectrometry) to obtain robust temporal information on their age and tempo of intrusion. These data enable us for the first time to define three intrusive episodes of 1-2 Ma each, separated by quiet periods of several Ma. The Aue-Schwarzenberg suite represents the oldest granites that intruded at similar to 323-322 Ma followed by the granites from Bergen and Kirchberg 2-4 Ma later. The highly evolved ore-bearing granites from the Eibenstock pluton intruded after a time lag of similar to 5 Ma at similar to 315-314 Ma. The new data show that there is a resolvable age difference between the two known granite groups. Granite group 2 (also assigned as younger igneous complex, represented by the Eibenstock pluton) is >= 5 Ma younger than granite group 1 (assigned as older igneous complex, represented by granites from Aue-Schwarzenberg, Bergen and Kirchberg).