Soda-rich pyroxenes in felsic rocks from the Warrumbungle Volcano, central New South Wales, contain up to 14.5 wt. ~ ZrO 2, which is more than double the previously reported maximum ZrO2 in pyroxene. Zr is believed to enter aegirine as the component Na(Fe2+,Mn,Mg)0.sZro.sSi206 via the coupled substitution: (Fe 2 +,Mn,Mg)Vl+ Zr vJ = 2(Fe a +)Vl. This component exceeds 50 mol. % in some analyses.Pronounced pyroxene Zr-enrichment is restricted to rocks in which sodic amphibole is the major ferromagnesian mineral, with pyroxene only a minor late-stage phase. The Zr-rich pyroxenes resulted from a combination of host lava peralkalinity, low oxygen fugacity, rapid disequilibrium crystallization and low mobility of the Zr ion. These factors collectively led to the development of interstitial Zr-enriched microdomains in the felsic hosts during their final stages of crystallization.
ABSTRACT. Babingtonite is a common constituent of calcareous volcanic detritus in the interstices of pillow lavas from an outcrop of the Takitimu Group, western Southland, New Zealand, Associated minerals include Fe-rich prehnite (Fe/(Fe+A1) = 0.12-0.33), Fe-rich epidote (Ps2,_53), grandite garnet {av. Andradite70 Grossular30), quartz, calcite, chlorite, and pumpellyite. Babingtonite shows little departure from its ideal composition other than minor Mg, Mn, and A1 and a trace of Na.Textural evidence and microprobe data suggest that the babingtonite, Fe-rich epidote, calcite, and quartz formed from hydrothermal solutions by direct precipitation in open cavities and by replacement of highertemperature silicate phases (in particular plagioclase and basaltic glass) in a shallow marine volcanic environment. During subsequent burial and low-grade metamorphism babingtonite was partially replaced by prehnite, less Fe-rich epidote, grandite, and chlorite.
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