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A predictive model for divalent element partitioning between clinopyroxene and basaltic melt and a Europium-in-Plagioclase-Clinopyroxene Oxybarometer for cumulate rocks
- Award ID(s):
- 2054551
- PAR ID:
- 10640769
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Geochimica et cosmochimica acta
- ISSN:
- 0016-7037
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Several geothermobarometric tools have focused on clinopyroxene due to its prevalence in igneous rocks, however clinopyroxene produced in high-silica igneous systems is high in iron and low in aluminum, causing existing geothermometers that depend on aluminum exchange to fail or yield overestimated temperatures. Here we present a new clinopyroxene-liquid geothermometer recommended for use in natural igneous systems with bulk SiO2 ≥ 70 wt%, which contain clinopyroxene with Mg# ≤ 65 and Al2O3 ≤ 7 wt%. (1) T ( ∘ C ) = 300 [ − 1.89 − 0.601 ( X CaTs Cpx ) − 0.186 ( X DiHd 2003 Cpx ) + 4.71 ( X SiO 2 liq ) + 77.6 ( X TiO 2 liq ) + 10.9 ( X FeO liq ) + 33.6 ( X MgO liq ) + 15.5 ( X CaO liq ) + 15.6 ( X KO 0.5 liq ) ] The new geothermometer lowers calculated temperatures by ~85 °C on average relative to Putirka (2008, Eq. 33) and reduces the uncertainty by a factor of two (standard error of estimate ±20 °C). When applied to natural systems, we find this new clinopyroxene-liquid geothermometer reconciles many inconsistencies between experimental phase equilibria and preexisting geothermometry results for silicic volcanism, including those from the Bishop Tuff and Yellowstone caldera-forming and post-caldera rhyolites. We also demonstrate that clinopyroxene is not restricted to near-liquidus temperatures in rhyolitic systems; clinopyroxene can be stable over a broad temperature range, often down to the solidus. An Excel spreadsheet and Python notebook for calculating temperature with this new geothermometer may be downloaded from GitHub at http://bit.ly/cpxrhyotherm.more » « less
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