Intersector element partitioning in tourmaline: a potentially powerful single crystal thermometer |
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| Authors: | Vincent J van Hinsberg John C Schumacher |
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| Institution: | (1) Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol, BS8 1RJ, UK |
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| Abstract: | Hourglass sector zoning, and related polar overgrowths, are common features of metamorphic tourmaline, developing as a result
of variations in element preference on the different growth surfaces. For sector-zoned crystals, three domains are present
for each growth zone (c
+, c
− and a), with compositional differences most distinct for Ca and Ti, and among c
+
and c
−
sectors. Intersector differences vary, commonly showing decreasing fractionation from core to rim attributed to increasing
metamorphic grade. Here we show that intersector element partitioning is temperature dependent and derive empirical geothermometers
based on c
+
–c
−
and c
+
–a partitioning of Ca and Ti. These thermometers are applicable over a range of temperatures and bulk-rock compositions. Intersector
partitioning is not affected by re-equilibration and records and preserves complete T-histories of individual tourmaline grains from prograde to peak and on to retrograde growth. Information on element mobility
is preserved by tourmaline composition, because intersector partitioning is independent of element concentration. These factors
make intersector partitioning an ideal tool to elucidate the thermal history of tourmaline grains and thus their host environment
and tourmaline’s refractory nature preserves these signatures even into the sedimentary record.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. |
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| Keywords: | Intersector Geothermometer Tourmaline Sector zoning Thermal history |
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