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Mössbauer spectroscopy of omphacite and garnet pairs from eclogites: Application to geothermobarometry

Authors: Zheng, YF; Fu, B; Li, YL;

Mössbauer spectroscopy of omphacite and garnet pairs from eclogites: Application to geothermobarometry

Abstract

Cation partition among coexisting minerals has been widely applied to eclogite thermometry, but an accurate estimation of Fe 3+ content compared to total Fe is crucial in obtaining reasonable temperatures for petrologic studies. Room-temperature Mossbauer spectroscopy was measured for garnet-omphacite pairs in high-pressure (HP) and ultrahigh-pressure (UHP) eclogites from the Dabie terrane in east-central China. The results show very low Fe 3+ /∑Fe ratios of 0.026 to 0.082 in garnet but high Fe 3+ /∑Fe ratios of 0.240 to 0.689 in omphacite. The hyperfine parameters of minerals record the HP-UHP conditions that the eclogites experienced. Fe 2+ in clinopyroxenes with low Na + Ca contents in their M2 sites shows pressure-induced occupation in M1 site. The quadrupole splitting of Fe 2+ in HP-UHP garnets (3.61 to 3.77 mm/s) and omphacites (2.77 to 3.06 mm/s) are among the highest values ever reported, indicating effectively pressure-regulated polyhedral sites. After the Fe 3+ was corrected, Fe 2+ -Mg partitioning not only significantly narrow the ranges relative to those without Fe 3+ correction, but also yield temperatures about 8 to 370 °C lower than the uncorrected temperatures for the same garnet-pyroxene pairs. The recalculated temperatures are constrained to narrow ranges of 477 to 647 °C for quartz-bearing eclogites and 624 to 843 °C for coesite-bearing eclogites. These maximum values provide close proxies to peak metamorphic temperatures provided that the retrograde exchange of Fe-Mg cations by diffusion between minerals during exhumation is taken into account.

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China (People's Republic of)
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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
36
Top 10%
Top 10%
Top 10%
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