Fachbereich 14 - Geowissenschaften
Institut für Planetologie
Analytische Planetologie

Mikrostrukturen von Datierungsmineralen:
Welchen Einfluß haben sie au die geologische Signifikanz radiometrischer Alter?

Dating with the U-(Th)-Pb, Rb-Sr, and K-Ar decay systems is one of the most fundamental techniques in geoscience. Yet frequently disturbances in the isotope systems of the dated minerals hamper an assessment of the geologic relevance of the measured data ("ages"). Such disturbances include partial loss of radiogenic isotopes, and parent-daughter element fractionation. These effects are explained by diffusion along lattice defects, re-crystallization, dissolution - precipitation processes, and most popular, by volume diffusion. The latter process stood in the center of most experimental and theoretical studies in the field of "opening and resetting of isotope systems", whereas, the essential role of the minerals micro-structures is persistently underestimated. - We analyze in this project systematically the micro-structures of the classic dating minerals monazite, titanite, rutile (U-Pb), as well as mica (Rb-Sr, ³⁹Ar-⁴⁰Ar) from well-dated mineral populations with transmission electron microscopic (TEM), X-ray (XRD), cathodoluminescence and Raman techniques. Novel analytical approaches include the use of the site specific focused ion beam preparation technique for TEM, as well as XRD and TEM in-situ annealing experiments The expected outcome from the research project is a better understanding of mechanisms enabling or forcing the opening or resetting of isotopic clocks in minerals. The results may gain basic importance for nuclear waste deposits.

Drittmittelgeber:

Deutsche Forschungsgemeinschaft

Beteiligte Wissenschaftler:

Deutsch, A. (Leiter), Schärer, U. (Univ. Nice), Seydoux-Guillaume, A.-M., Wirth, R. (GFZ, Potsdam)

Veröffentlichungen:

Seydoux-Guillaume, A.-M., Goncalves Ph., Wirth R., Deutsch, A. (2003): Focus ion beam technique - state-of-the-art tool for TEM study of polyphased discordant monazites. Geology, submitted.

Seydoux-Guillaume, A.-M., Wirth, R., Deutsch, A., Schärer, U. (2002): On the microstructure of monazite: implications for its ability to immobilise nuclear waste. 18th gen. Meeting Int. Mineral. Ass., September 2002, Edinburgh, Scotland, 294.

Seydoux-Guillaume, A.-M., Wirth, R., Deutsch, A., Schärer, U. (2002): On the importance of looking at the microstructure of U-Pb dating minerals. Geochim. Cosmochim. Acta 66, 15A, A699.