Geochronology is the science of dating the occurrence of events in the history of the Earth and of determining the temporal rates of geological processes. By measuring the amount of radiogenic "daughter" isotopes produced by radioactive decay from a “mother” isotope with a known half-life, geologists can establish the “absolute age”, i.e, the age in absolute units of time (Ma, ka, etc.) for the parent material. A number of radioactive isotopes from different elements, such as uranium, thorium, rhenium, samarium, lutetium, rubidium and potassium are used for this purpose. Earth Scientist can rely on a wide variety of geochronological tools or methods to allow the “absolute” dating of rocks and minerals. Techniques exist to date practical all geological materials, from billions of years in age to historical records. For instance: U-Pb (decay of 238U -> 206Pb, 235U -> 207Pb) and Th-Pb (232Th -> 208Pb) geochronology of zircon, monazite, and xenotime is used for determining the age of emplacement of igneous, mostly granitoid rocks. U-Th-Pb ages of metamorphic minerals, such as zircon, sphene and monazite can be used to date high temperature thermal events, including terrestrial meteoritic impacts, and to determine thermochronologic histories of terranes. Sm-Nd (147Sm -> 143Nd) ages on garnet, pyroxene and amphibole are most useful to constrain high-pressure events reflecting eclogitisation of oceanic and continental crust and to date the formation of basic intrusive rocks such as gabbros. Rb-Sr (87Rb -> 87Sr), Ar-Ar (40K -> 40Ar), Fission track, and Uranium-Thorium-Helium (U/Th)-He mineral ages are all well suited to date the cooling of a rock unit in range of ca. 500 °C to 70 °C. 147Sm/143Nd, 176Lu/176Hf, 87Rb/87Sr, and 187Re/187Os isotope data help to distinguish different mantle and crustal reservoirs and allow the reconstruction of the evolution of these reservoirs.
From the large number of different geochronological methods the following are currently used in our laboratory:
Our work is concentrated on material from the Alps, the Himalayan-Tibet orogenic belt and the wider Mediterranean area.
The Sm-Nd method is a vital isotope analytical tool to approach both petrogenetic as well as geochronological questions.
U-Pb and Th-Pb dating of accessory minerals by in-situ
U-Th-Pb isotope analysis by Laser-Ablation Inductively Coupled Mass Spectrometry (LA-ICP-MS) and Secondary Ion Mass Spectrometry (SIMS).
Laboratories and Instrumentation
The GeoCosmoChron division of the Department of Lithospheric Research is equipped with all the necessary facilities to allow state-of-the-art geochronological and isotope geochemical research.
The following dating and isotope crystal-chemical techniques are used in our laboratory:
- In-situ U-Pb dating of separated zircons, monazite, xenotime, apatite, rutile, sphene etc. by LA-ICP-MS and SIMS techniques.
- In-situ Th-Pb dating of separated monazite, xenotime, rutile, sphene etc. by LA-ICP-MS techniques.
- True in-situ dating in petrographic thin-section of the above mentioned minerals.
- In-situ major, trace and REEs concentration analysis of zircon, monazite, xenotime, apatite etc by LA-ICP-MS techniques.
- Hf isotope systematics of zircon.
Contact: Urs Klötzli