Geochronology

CHRO's activities are to be considered within the frame of the mineral environment field. The origin of rocks and mineral deposits, the structural evolution of the crust are addressed by means of the study of argon accumulation upon radioactive decay of potassium, in different geological systems. This provides a very versatile dating tool, encompassing the whole earth's history. A careful investigation of the conditions for argon retentivity in different mineral structures allows the deciphering of the thermal history of the rock sample, whenever the latter underwent a long crustal evolution. This means for example that the processes of mountain-building and destruction upon erosion can be quantitatively modellised on the base of experimentally determined physical parameters. Ar-Ar geochronology, a variant of conventional K-Ar dating, indeed allows refined interpretations, being based on sophisticated physical methods (mass spectrometry, neutron activation and laser fusion and ablation). The applications are thus numerous: the dating of the ore deposits provides a clue for ore prospection, active faults (possible seats of earthquakes) can be identified, etc. Let us mention in particular the establishment of a numerical chronology for Quaternary sedimentary sequences (from 2 million years to 2000 years) which keep the record of past climate changes.