ORIGINAL PAPER Raman-based geobarometry of ultrahigh-pressure metamorphic rocks: applications, problems, and perspectives Andrey V. Korsakov & Vladimir P. Zhukov & Peter Vandenabeele Received: 27 November 2009 / Revised: 27 April 2010 / Accepted: 5 May 2010 / Published online: 26 June 2010 # Springer-Verlag 2010 Abstract Raman-based geobarometry has recently become increasingly popular because it is an elegant way to obtain information on peak metamorphic conditions or the entire pressure-temperature-time (P-T-t) path of metamorphic rocks, especially those formed under ultrahigh-pressure (UHP) conditions. However, several problems need to be solved to get reliable estimates of metamorphic conditions. In this paper we present some examples of difficulties which can arise during the Raman spectroscopy study of solid inclusions from ultrahigh-pressure metamorphic rocks. Keywords Raman spectroscopy . Thermoelastic model . Coesite . Quartz . Aragonite . Calcite Introduction Recovery of peak metamorphic conditions for ultrahigh- pressure metamorphic (UHPM) rocks is a big challenge, because frequently these rocks undergo nearly isothermal decompression hiding any sign of the UHP stage. Coesite and diamond are the best mineral indicators that the mineral assemblages in crustal-derived metamorphic rocks were formed at depths of more than 90 km and more than 120 km, respectively [1–3]. Raman spectroscopy was originally used to prove the presence of relics via UHP mineral indicators (e.g., diamond or coesite) [1–4]. Only recently has the pressure dependence of the Raman bands started to be used as a new type of geobarometer [5–7]. For instance very high residual pressure was confirmed by Raman spectroscopy for different solid phase inclusions in refractory minerals (e.g., diamond, garnet, kyanite, zircons) formed in the coesite or diamond stability field (see [5–11] and references therein). It is noteworthy that coesite inclusions in refractory minerals (e.g., garnet, kyanite, zircon, clinopyroxene) from different UHPM complexes exhibit different degrees of retrogression to quartz [1, 2, 8, 11]. Raman spectroscopic study of these two SiO 2 polymorphs clearly indicates different residual pressure within the single inclusions of 2.0–2.3 GPa for coesite and 0.8–1.5 GPa for quartz, respectively [6, 8, 10, 11]. This discrepancy is inconsistent with local equilibrium postulates, which are milestones of metamorphic petrology. Furthermore despite the presence of a strong optical halo in the host garnet around such bimineralic coesite-quartz inclusions (Figs. 1, 2 and 3) no measurable overpressure was documented by Raman spectroscopy in the host garnet adjacent to inclusions [8]. Complex aragonite-calcite inclusions in garnet from diamond-bearing calcite marbles without measurable up- shift of Raman bands for both polymorphs of CaCO 3 clearly indicate very low values of overpressure for the aragonite and calcite [12]. Lack of overpressure for these inclusions is inconsistent with their UHPM origin. However, A. V. Korsakov (*) Institute of Geology and Mineralogy of Siberian Branch of the Russian Academy of Sciences, Koptyug Pr. 3, Novosibirsk 630090, Russia e-mail: korsakov@igm.nsc.ru e-mail: korsakov@uiggm.nsc.ru V. P. Zhukov Institute of Computational Technologies of Siberian Branch of the Russian Academy of Sciences, Acad. Lavrentjev avenue 6, 630090 Novosibirsk, Russia P. Vandenabeele Department of Archaeology, Ghent University, Sint-Petersnieuwstraat 35, 9000 Ghent, Belgium Anal Bioanal Chem (2010) 397:2739–2752 DOI 10.1007/s00216-010-3831-4