Microprobe-based monazite dating in the Alpine Basement

Monazites are important natural rare-earth phosphates (ideal formula CePO4). They occur in many rocks as small, accessory crystals. Because of their ability to incorporate the radioactive elements Th and U, which decay to Pb isotopes by time, monazite crystals can be used for age determinations of rocks. One possibility to determine the formation age of a monazite is to analyse its Th, U and Pb content by means of the electron microprobe and to calculate a so-called chemical age. This new method is established at the University of Salzburg since some years. In the frame of this project it shall be systematically applied to basement rocks (granite gneisses, paragneisses) in the Eastern Alps. It is expected that the data obtained by this method will constitute an important new contribution for the understanding of the early (Pre-Mesozoic) geological history of the Alps.

Monazites are important natural rare-earth phosphates (ideal formula CePO4). They occur in many rocks as small, accessory crystals. Because of their ability to incorporate the radioactive elements Th and U, which decay to Pb isotopes by time, monazite crystals can be used for age determinations of rocks. One possibility to determine the formation age of a monazite is to analyse its Th, U and Pb content by means of the electron microprobe and to calculate a so-called chemical age. This new method is established at the University of Salzburg since some years. In the frame of this project it shall be systematically applied to basement rocks (granite gneisses, paragneisses) in the Eastern Alps. It is expected that the data obtained by this method will constitute an important new contribution for the understanding of the early (Pre-Mesozoic) geological history of the Alps.