Dating multiply overprinted Sn-mineralized granites—examples from the Erzgebirge,Germany |
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Authors: | Rolf L Romer Rainer Thomas Holly J Stein Dieter Rhede |
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Institution: | (1) GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany;(2) AIRIE Program, Department of Geosciences, Colorado State University, Fort Collins, CO 80512-1482, USA;(3) Geological Survey of Norway, 7491 Trondheim, Norway |
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Abstract: | Granites and primary tin mineralization in the Erzgebirge were dated using (1) conventional U–Pb dating of uraninite inclusions
in mica, (2) Rb–Sr dating of inclusions in quartz that represent highly evolved melts, (3) Re–Os dating of magmatic–hydrothermal
molybdenite, and (4) chemical Th–U–Pb dating of uraninite. Conventional isotope dilution and thermal ion mass spectrometry
and chemical Th–U–Pb dating of uraninite in granites from the Ehrenfriedersdorf mining district provide ages of 323.9 ± 3.5
Ma (2σ; Greifenstein granite) and 320.6 ± 1.9 and 319.7 ± 3.4 Ma (2σ, both Sauberg mine), in agreement with U–Pb apatite ages of 323.9 ± 2.9 and 317.3 ± 1.6 Ms (2σ, both Sauberg mine). Rb–Sr analysis of melt inclusions from Zinnwald gives highly radiogenic Sr isotopic compositions that,
with an assumed initial Sr isotopic composition, permit calculation of precise ages from single inclusions. The scatter of
the data indicates that some quartz-hosted melt inclusions have been affected by partial loss of fluid exsolved from the melt
inclusion. Re–Os dating of two molybdenite samples from Altenberg provides ages of 323.9 ± 2.5 and 317.9 ± 2.4 Ma (2σ). Together with age data from the literature, our new ages demonstrate that primary tin mineralization and the emplacement
of the large Sn-specialized granites in the Erzgebirge fall in a narrow range between 318 and 323 Ma. Primary Sn mineralization
occurred within a short interval during post-collisional collapse of the Variscan orogen and was essentially synchronous over
the entire Erzgebirge. In contrast to earlier claims, no systematic age difference between granites of the eastern and western
Erzgebirge was established. Furthermore, our data do not support a large age range for Late-Variscan granites of the Erzgebirge
(330–290 Ma), as has been previously suggested. |
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Keywords: | U– Pb Rb– Sr Re– Os Uraninite Mineral inclusion Melt inclusion Molybdenite Erzgebirge |
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