U-Pb age of rutile from the eclogite xenolith of the Udachnaya kimberlite pipe

Abstract

861 The Udachnaya kimberlite pipe in the Daldyn kimberlite field (Daldyn–Alakit region) of the central part of the Yakutian diamond province is the largest diamond deposit in Russia and one of the largest in the world. The pipe consists of two conjugate bodies: Udachnaya East and Udachnaya West. As is evident from the U–Pb dating of perovskites from kimberlites, the ages of the Udachnaya pipe formation are 367 ± 3 and 367 ± 5 Ma (Udachnaya East); 361 ± 4 and 353 ± 5 Ma (Udachnaya West) [1]. Deep seated xenoliths of mantle rocks in kimber lite pipes are represented by a wide spectrum of ultra basic rocks, as well as pyroxenites and eclogites. Eclogites are coarse granular rocks mostly composed of garnet and clinopyroxene with accessory rutile. In addition to bimineral eclogites, the most abundant among xenoliths of the basic composition, there are corundum and kyanite eclogites [2]. Numerous stud ies of eclogite xenoliths from the Udachnaya kimber lite pipe have provided evidence for the influence of mantle metasomatism on the upper mantle rocks and have distinguished some signs of metasomatic origin of diamonds [3, 4]. However, the age of these processes has been not determined to date. Because of this, we have performed the dating of rutiles from the eclogite xenolith (Sample UD 208 05) entering the composi tion of the secondary mineral association. Eclogite xenolith from the Udachnaya pipe (Sam ple UD 208 05) is bimineral eclogite composed of dark green xenomorphic clinopyroxene (3–6 mm) and round garnet (2–5 mm) grains reaching ~55 and ~44 vol %, respectively. The xenolith contains the areas of partial melting including veins crossing rock forming omphacite and garnet, which consist of amor phous material (silicate glass) and products of its replacement (chlorite and quartz). These areas are surrounded by replaced omphacite with the typical “sponged textures” (symplectites) [3]. Among the accessory minerals are rutile, ilmenite, and pyrrhotite. The chemical composition of minerals was analyzed by energy dispersive spectrometry on a Tescan MYRA 3 LMU electron microscope with an EDS detector (Oxford Instruments) and using a JEOL JXA 8100 X ray microanalyzer at the Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences.