A mechanism for Nb incorporation in rutile and application of Zr-in-rutile thermometry: A case study from granulite facies paragneisses of the Mogok metamorphic belt, Myanmar

Abstract

Rutile grains occur extensively in host phases of biotite and quartz-feldspar aggregate in high-temperature paragneisses of the Mogok metamorphic belt of Myanmar. They occur as an isolated phase and sometimes show intergrowth texture with ilmenite. Most rutile grains contain up to 3.7 wt.% Nb2O5, which shows positive correlations with Fe and trivalent elements. Niobium substitutes for Ti by a coupled substitution with the trivalent cations (M3+) of Nb5+M3+Ti4+-2. Fine-grained rutile grains included in ilmenite are distinctly poor in Nb (<0.1 wt.% as Nb2O5) and contain Fe of 1.7–3.2 wt.% as Fe2O3, suggesting vacancybearing substitution of Fe3+4 Ti4+-3□–1, where □ indicates a vacancy. The rutile grains in the felsic phases contain high Zr contents of up to 4200 ppm, suggesting equilibrium temperatures over 800°C using the Ti-in-rutile geothermometer. These high-temperature conditions are consistent with those estimated by conventional methods reported in the literature and suggest widespread occurrences of the upperamphibolite and granulite facies metamorphic rocks in the middle segment of the Mogok metamorphic belt. In contrast, the Zr contents of rutile grains in biotite are usually <1000 ppm, implying equilibrium temperatures lower than 750°C. Most of the rutile grains poorer in Zr might have been included in biotite and were isolated from the zircon-bearing system during an early stage of prograde metamorphism. Some other rutile grains poorer in Zr might have been an exsolved phase from Ti-rich biotite during retrograde metamorphism, which was furthered by the infiltration of metamorphic fluid under lower-amphibolite facies conditions.

Niobium mineralization of sedimentary carbonates, Lewisian Complex, UK

“…However, the mineralization in the Loch Shin marble appears to relate to the chemistry of the Caledonian plutons that intruded the region surrounding Loch Shin. In particular, the alkaline complexes at Loch Borralan and Loch Loyal, both 30 km distant, are both notably enriched in REE (Walters et al 2013;Abdulkadir et al 2020) Data from Garson et al (1984), Rock and Waterhouse (1986), , Rock (1987), Young et al (1994), Walters et al (2013), Zhong et al (2015), Win et al (2017).…”

Rutile Mineral Chemistry and Zr-in-Rutile Thermometry in Provenance Study of Albian (Uppermost Lower Cretaceous) Terrigenous Quartz Sands and Sandstones in Southern Extra-Carpathian Poland

“…The use of EPMA in trace mode is facilitated by the high thermal stability of rutile, thanks to which it is possible to increase the detection limit of the determined trace elements by using the higher current of the electron beam and the extending count time at peak and background positions. Approximate concentrations of elements from the HFSE group (high field strength elements), represented by Nb, Ta, Zr, Hf, and W, as well as some transition metals group, such as Cr, V, and Fe, can reach concentrations up to 3000 ppm [30,33,54,63,64]. Zr concentrations in rutile from metamorphic rocks vary in the wide range from several ppm up to 11,000 ppm [29,34,65].…”

Drastic effect of shearing on graphite microtexture: attention and application to Earth science

“…We used a graphite grain in sample S26 that was collected from granulite facies region of Mogok metamorphic belt, Myanmar, which is located along the western margin of the Shan-Tai block. The sample S26 is a garnet-biotite-sillimanite gneiss, and its petrological and mineralogical characteristics were documented by Maw Maw Win et al (2017). It is composed mainly of garnet, biotite, plagioclase, quartz, and sillimanite, with minor graphite, rutile, ilmenite, apatite, monazite, and zircon.…”