Ilmenite-bearing mantle parageneses from kimberlite pipes
International Kimberlite Conference Extended Abstracts: 2008
Ilmenite-bearing varieties are scarce among mantle inclusions, found in kimberlite pipes of the Yakutian Province. We studied the composition of the representative collection of samples (over 50) of ilmenite xenoliths, forming a wide spectrum of petrographic varieties, including dunites, harzburgites, wehrlites, lherzolites, pyroxenites, eclogites, websterites, glimmerites from pipes Mir (Malya Botuobia field), Udachnaya, Dalnya (Daldyn field), Obnazhennaya, Sludyanka, Poiskovaya (Kuoika
... Below we briefly describe principal features of chemical composition of rock-forming minerals and give an estimation of PT-parameters of crystallization. Silicates demonstrate as a rule high FeO content, relatively low Cr 2 O 3 and high TiO 2 concentrations. Olivine (Ol) is characterized by high iron content: its average composition corresponds to the concentration as 13,8 % of fayalite minal, varying within 9,3 -18 %. Deep-seated xenoliths without ilmenite contain high-magnesium Ol, as a rule, with 6 -12 % of fayalite minal. Garnet (Gar) demonstrates high FeOtotal (from 10-12 to 18,32 wt. %) and wide variations in concentrations of others oxides (0,12-1,44 wt. % TiO 2 , 0,19-6,55 wt. % Cr 2 O 3 ). Figurative points of Gar composition in СаО-Cr 2 O 3 plot (Sobolev, 1974) are mainly concentrated close to the lherzolite trend (Fig. 1A) . Gar from different pipes is characterized by wide variations in TiO 2 content ( fig. 1b) at relatively slight variations in magnesium content (69 -81 %). Despite a significant range in TiO 2 variations in Gar of Sludyanka pipe (0,12-1,44 wt. %), the basic part of the investigated grains is grouped in the most low-titanium area (Fig. 1B) . Garnet with higher titanium concentration (0,3-0,5 wt. %) is found in Obnazhennaya pipe; and Gar demonstrating the highest titanium content (0,6 <TiO 2 <1,2 wt. %) is observed in Udachnaya and Poiskovaya pipes. Clinopyroxene (Cpx) includes subcalcium diopsides, diopsides, low-chromium diopsides (by Stephens, Dawson, 1977) and is characterized by the increased concentrations of FeO (2,77-6,12 wt. %) and TiO 2 (0,19 -1,06 wt. %), low Cr 2 O 3 (0,15-1,10 wt. %) content.