Publication Date:
2022-05-26
Description:
Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Chemical Geology 393-394 (2015): 79-92, doi:10.1016/j.chemgeo.2014.11.014.
Description:
A REE-in-garnet-clinopyroxene thermobarometer for eclogites, granulites, and garnet
peridotites has been developed on the basis of the temperature, pressure and mineral composition
dependent partitioning of rare earth elements (REEs) between garnet and clinopyroxene. This
new thermobarometer is derived from the garnet-clinopyroxene REE partitioning model of Sun
and Liang (2014) that was calibrated against experimentally determined garnet-melt and
clinopyroxene-melt partitioning data. It makes use of a group of trace elements that have similar
geochemical behaviors at magmatic and subsolidus conditions, and allows one to invert
temperature and pressure simultaneously using a least squares method. Application of the REE-in-garnet-clinopyroxene thermobarometer to REE partitioning data from laboratory experiments
and field samples (quartz-bearing, graphite-bearing, and diamond-bearing granulites and eclogites;
and well-equilibrated mantle eclogite xenoliths) published in the literature validates its reliability
at both magmatic and subsolidus conditions. Application of the new thermobarometer to eclogites,
garnet granulites and peridotites from various tectonic settings reveals an intriguing observation:
temperatures derived from the REE-based thermobarometer are consistently higher than those
derived from the widely used Fe-Mg thermometer of Krogh (1988) for samples that experienced
cooling, but systematically lower than temperatures derived from the Fe-Mg thermometer for
samples from thermally perturbed tectonic settings. The temperature discrepancies are likely due
to the relative differences in diffusion rates between trivalent REEs and divalent Fe-Mg in garnet
and clinopyroxene. Temperatures derived from the REE-based thermometer are closely related to
closure temperatures for samples that experienced cooling, but are likely equilibrium or apparent
re-equilibration temperatures at an early stage of heating for samples from thermally perturbed
tectonic environments. The REE-in-garnet-clinopyroxene thermobarometer can shed new light on
thermal histories of mafic and ultramafic rocks.
Description:
This work
was supported in part by the NSF grant EAR-1220076 and NASA grant NNX13AH07G.
Keywords:
Thermobarometer
;
Garnet
;
Clinopyroxene
;
Eclogite
;
Granulite
;
Garnet peridotite
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
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