ANTIQUITY OF PERIDOTITIC DIAMONDS FROM THE SIBERIAN CRATON

Abstract

Diamonds erupted by kimberlites traversing ancient continental tectosphere [1] provide a window into the evolution of continents and their mantle keels. However, the vintage of this window; that is, the timing of crystallization of peridotitic mineral inclusion-bearing diamonds beneath different cratons, has proved controversial because of the model age arguments involved [2–12]. Isochron age data for peridotitic garnets in combination with nitrogen aggregation data for host diamonds from the Udachnaya kimberlite on the Siberian craton show that such diamonds are ancient and could not have crystallized as recently (< 70 ka before eruption) as proposed [10–12]. The garnets yield a SmNd isochron age of 2.0 Ga and the diamonds display nitrogen aggregation characteristics requiring lithospheric mantle storage at temperatures of 1100–1200°C for a comparable period. The crystallization age of these ‘peridotitic’ diamonds is similar to that of equivalent diamonds from the Premier kimberlite on the Kaapvaal craton, which postdate the massive 2.05 Ga old Bushveld Complex and represent a diamond generation unrelated to craton keel stabilization 3.2 Ga ago [3,9,10].