New geochronometer for the direct isotopic dating of native platinum minerals (Pt-190-He-4 method)

作者：Shukolyukov Yu A^*; Yakubovich O V; Mochalov A G; Kotov A B; Sal' nikova E B; Yakovleva S Z; Korneev S I; Gorokhovskii B M

来源：Petrology, 2012, 20(6): 491-505.

DOI：10.1134/S0869591112060033

A new method of isotope geochronology was proposed for dating native platinum minerals on the basis of the alpha-decay of the natural isotope Pt-190. The analysis of the thermal desorption of helium in the crystal lattice of native metals, including platinum, allowed us to predict a very high thermal stability (retentivity) of radiogenic He-4 in native platinum minerals up to their melting temperatures. In order to validate the proposed Pt-190-He-4 method, direct isotopic dating was performed for isoferroplatinum from the Galmoenan dunite-clinopyroxenite and Kondyor alkaline ultramafic massifs. The results of dating obtained by this method for primary ore platinum from the Galmoenan Massif (70 +/- 5 Ma) are consistent with geological observations and mean Sm-Nd and Rb-Sr isotopic age estimates. The Pt-190-He-4 age obtained for placer isoferroplatinum from the Kondyor Massif (112 +/- 7 Ma) also agrees with geological observations and is close to the K-Ar and Rb-Sr ages of koswites (phlogopite-magnetite pyroxenites, gabbros, nepheline syenites, and metasomatic rocks after dunites). Our experimental data demonstrated that the Pt-190-He-4 method is a promising tool for dating native platinum minerals.

• 出版日期2012-11