Isotope geology

The basic process of radioactive decay system Source: BGR

Rocks and minerals contain natural radioactive elements which decay at specific constant rates. Consequently, the composition of the material changes within time. The science of geochronology depends on such mechanisms. Isotope chemistry and geochronological investigations on rocks and minerals provide geoscientists with answers to questions on various petrogenetic, mineral deposit and paleoclimatic issues.

At the Federal Institute for Geosciences and Natural Resources the age of minerals and rocks are determined by established methods of isotope ratio determination like rubidium-strontium, samarium-neodymium and uranium-lead. The aim is the dating of geological processes such as mineral deposition, intrusions, volcanism or metamorphic events. Isotope chemical methods are also used to examine magmatic, metamorphic and sedimentary substance transport and exchange processes, which play a major role in the development of mineral deposits and in their alteration. Isotope analysis is also an important exploration tool, since it allows the determination of the origin of rocks and mineral deposits. In research on marine geological processes scientists apply the strontium isotope method to date marine sediments.

First of all, the relevant elements are chemically separated from the collected samples in a laboratory clean-room. Scientists then analyse the isotopic composition of the samples by thermal ionization mass spectrometry. Finally, the age of the mineral or rock forming processes is calculated from the parent-daughter isotope proportions for a radioactive decay system, taking into account the specific half-lives.

The Federal Institute for Geosciences and Natural Resources is in the process of broadening its spectrum of methods: in future, the calcium isotope method will be used for the investigation of paleoclimatic questions.

Activities in isotope geology are focused on research projects in the Antarctic and Arctic, marine geological exploration of active and passive continental margins, research on metallic raw materials and technical co-operation projects.