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RUTILE AND QUARZ INCLUSIONS IN ECLOGITIC GARNETS FROM THE BULKUR ANTICLINE OF THE NORTNEASTERN SIBERIAN PLATFORM

Anastasia Biller

Abstract

Inclusions in diamond associated minerals are additional information about the formation of minerals in the depths of the mantle. Considerable attention is paid to the study of rutile inclusions in garnets in literature. Until now, there is no consensus on formation of oriented needle-like inclusions, some authors consider them to be epitaxial intergrowths, others ? exsolution. This article contains results of the study of eclogitic garnets from heavy fraction of diamondiferous volcanogenic sedimentary rocks of the Bulkur anticline (North-east Siberian platform). The garnets are characterized by pyrope-almandine composition and generally belong to garnets of bimineral eclogites (content of Cr2O3 0-0.84 wt. %, Fe?tot of 19.86-25.58 wt. %). Inclusions of apatite, rutile, feldspar and quartz are identified in garnets by Raman spectroscopy. The chemical composition of some surface inclusions was analyzed. Quartz is presented by faceted or rounded inclusions, usually 20-40 ?m in size. It often occurs in intergrowths with rutile. Values of residual pressure in quartz inclusions were calculated (Pincl=0.09-0.45 GPa) according to the results of Raman spectroscopy. At the model temperature of garnet crystallization from 550В°C to 650В°C, values of pressure during the entrapment of quartz inclusions made up of 0.29 to 1.22 GPa. Special attention is paid to rutile inclusions, which are usually found as oriented inclusions with short- and long-prismatic forms with length of needles from 20 to 50 ?m, thickness - from 1 to 5 ?m. Raman spectra of needle-like and isometric inclusions of rutile differ in the intensity of the main bands, that is associated with their crystallographic orientation. In some rutile inclusions there was an admixture of zirconium.

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DOI resolver: doi.org/10.5593/sgem2018/1.4/s04.021

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