The use of Raman spectroscopy of quatrz inclusions in garnet for estimation of metamorphic pressure

Gulbin Yu. L., Vasiliev E. A.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2015. V. 144. N 6. P. 106-114

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Language: Russian

Abstract

This paper draws on a case study of use of Raman quartz-in-garnet or QuiG barometry for assessment of the pressure during formation of metamorphic rocks in the northern Cumpston Massif, southern Prince Charles Mountains, East Antarctica. The studied samples (metapelites, metapsammites, and metabasites) contain garnet porphyroblasts up to 1 cm in size with abundant quartz inclusions. The Raman shifts of the 464 cm^–1 α-quartz peak were measured in these inclusions to yield the pressure of their entrapment. Only quartz grains of 5—15 m in diameter, which are not exposed to the thin section surface, were chosen for analysis. Typically, they displayed Raman shifts ranging between 0.5 and 3.2 cm^–1 (±0.2). Several grains located in the central zones of garnet porphyroblasts shown negative shifts in the range from –0.4 to –0.7 cm^–1. Calculations of the entrapment pressure, which were based on spectroscopic data and take into account the host rock’s thermal history, have demonstrated a fast increase of P from 5 to 11—12 kbar as the temperature grows from 525 to 550 °С, followed by isobaric heating to 650 °С. The constrained Р—Т path correlates well with estimates of Р—Т metamorphic conditions obtained by mineral thermobarometry and pseudosection modeling.

Key words: Raman spectroscopy, QuiG geobarometry, garnet, quartz inclusions, amphibolites, East Antarctica.