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Raman mapping of coesite inclusions in garnet from the Kokchetav Massif (Northern Kazakhstan)

journal contribution
posted on 2023-05-18, 04:20 authored by Korsakov, AV, Hutsebaut, D, Theunissen, K, Vandenabeele, P, Stepanov, AS
Coesite inclusions occur in a wide range of lithologies and coesite is therefore a powerful ultrahigh-pressure (UHP) indicator. The transformation of coesite to quartz is evidenced by three optically well identifiable characteristics (e.g. palisade textures, radial crack patterns, polycrystalline quartz pseudomorphs). Under overpressure monomineralic coesite (on an optical basis), lacking the above transformation characteristics may survive. Raman micro-spectroscopy was applied on monomineralic coesite inclusions in garnet porphyroblasts from diamond-bearing garnet–clinozoisite–biotite gneisses of the Barchi-Kol area (Kokchetav Massif, Northern Kazakhstan). These coesite inclusions are euhedral and display a characteristic anisotropic hallo. However, Raman maps and separate spectra of these inclusions display shifted bands for coesite and quartz. Microscopically undetectable, quartz shows on the Raman map as a thin shell around coesite inclusion. Shift of the main coesite band allows to estimate their overpressure: coesite inclusions record 0–2.4 GPa in garnet and zircon. The quartz shell remains under lower pressure 0–1.6 GPa. The possible application of coesite and quartz Raman geobarometers for UHP metamorphic rocks is discussed.

History

Publication title

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Volume

68

Issue

4

Pagination

1046-1052

ISSN

1386-1425

Department/School

School of Natural Sciences

Publisher

Pergamon-Elsevier Science Ltd

Place of publication

The Boulevard, Langford Lane, Kidlington, Oxford, England, Ox5 1Gb

Rights statement

Copyright 2007 Elsevier

Repository Status

  • Restricted

Socio-economic Objectives

Diamond exploration

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