Les résultats d'un grand nombre de dosages de potassium et d'argon effectués sur des échan tillons standards sont présentés; les âges K‐Ar correspondant sont également calculés. Il s'agit d'une part de standards géochronologiques: la muscovite Berne 4M, la biotite LP6 et la phonolite MZ, d'autre part de standards géochimiques diffusés par le CRPG: la biotite Mica‐Fe, la phlogopite Mica‐Mg et le basalte BE‐N.

A procedure of volatile analysis in rocks which permits quantitative estimation of all the volatile species of any geological interest is presented and illustrated by several examples. Gas extraction is per formed either by vacuum crushing or heating. A separation line using cold traps, oxidation (CO to CO2) and reduction (H20 to H2) furnaces permits to separate several fractions. At the end of each separation phase the pressure in the line is measured with a capacitance manometer before analysis of the gas mix ture with a mass spectrometer. Calibration is done periodically using standard gases stored in gauged bottles. The detection limits are 0.5 to 1. X 10-' mot H2O, 0.3 x 10-' mol C02 and about 0 .2 x 10' mol for H2, N2, CO, CH4 and Ar. Further species like organic compounds, S02 and H2S are detected but not determined. In the case of H2O and C02 the reproducibility is better than 4% . The conjunction of vacuum crushing, stepwise heating and size fraction analysis permits to separate components like: dissolved, adsorbed and vesicle trapped. In particular, effects of adsorption have been evaluated: it is a serious problem for , species like CO2 and H2O with finely crushed material. H2 and CO detected after thermal extraction when organic compounds are present in the sample reflect organic decomposition rather than any thermodynamic equilibrium attained upon rock formation .