Timing of magmatic-hydrothermal activity in the Variscan Orogenic Belt: LA-ICP-MS U–Pb geochronology of skarn-related garnet from the Schwarzenberg District, Erzgebirge

Abstract

Here, we present in situ U–Pb laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) ages of andradite-grossular garnet from four magmatic-hydrothermal polymetallic skarn prospects in the Schwarzenberg District, Erzgebirge (Germany), located in the internal zone of the Variscan Orogenic Belt. Within the geochronological framework of igneous rocks and hydrothermal mineralization in the Erzgebirge, the obtained garnet ages define three distinct episodes of Variscan skarn formation: (I) early late-collisional mineralization (338–331 Ma) recording the onset of magmatic-hydrothermal fluid flow shortly after the peak metamorphic event, (II) late-collisional mineralization (~ 327–310 Ma) related to the emplacement of large peraluminous granites following large-scale extension caused by orogenic collapse and (III) post-collisional mineralization (~ 310–295 Ma) contemporaneous with widespread volcanism associated with Permian crustal reorganization. Our results demonstrate that the formation of skarns in the Schwarzenberg District occurred episodically in all sub-stages of the Variscan orogenic cycle over a time range of at least 40 Ma. This observation is consistent with the age range of available geochronological data related to magmatic-hydrothermal ore deposits from other internal zones of the Variscan Orogenic Belt in central and western Europe. In analogy to the time–space relationship of major porphyry-Cu belts in South America, the congruent magmatic-hydrothermal evolution in the internal zones and the distinctly later (by ~ 30 Ma) occurrence of magmatic-hydrothermal ore deposits in the external zones of the Variscan Orogenic Belt may be interpreted as a function of their tectonic position relative to the Variscan collisional front.

Irish Zn-Pb deposits – a review of the evidence for the timing of mineralization. Constraints of stratigraphy and basin development.

“…Comparison with the apparent polar wander path for Europe suggests an age of ca. 265 to 310 Ma for this remagnetization event, consistent with the timing of the Variscan orogeny (Reinhardt et al, 2022) We can therefore discount these magnetic ages as they all do not reflect mineralization ages and appear to be due to resetting during Hercynian orogenesis in the late Stephanian to early Permian (Figure 8).…”

Zircon and Garnet U–Pb Ages of the Longwan Skarn Pb–Zn Deposit in Guangxi Province, China and Their Geological Significance

“…This consistency suggests that the garnet U-Pb age obtained in this study is reliable and represents the mineralization age of the Longwan Pb-Zn deposit. In recent years, the method of using garnet for geochronological studies of skarn deposits has gained increasing recognition [42,43] and has been more widely applied [9,11], particularly in areas with multiple episodes of skarn activity and a lack of exposed intrusive bodies, where it has demonstrated good application results [10]. During the Late Early Cretaceous, the Longwan Pb-Zn deposit formed through contact metasomatic reactions that occurred during the intrusion of granitic porphyry into the Silurian limestone.…”

“…Recent research highlights the higher U-Pb closure temperature system (>850 • C) in garnets compared to other minerals [5], and the elevated levels of U and Pb in Andradite, fulfilling the LA-ICP-MS elemental testing requirements [6]. Consequently, garnets have garnered significant attention as subjects for geochronological research in the skarn deposits [1,[7][8][9][10][11].…”