Other
Scientific paper
Aug 1982
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982e%26psl..60...86g&link_type=abstract
Earth and Planetary Science Letters, Volume 60, Issue 1, p. 86-92.
Other
4
Scientific paper
A latite dome in northwest Arizona contains a rare occurrence of primary SO4-rich scapolite phenocrysts. The total phenocryst assemblage consists of plagioclase (An20-An33), hornblende, biotite, and scapolite (Me68). Microphenocrysts include allanite and oxidized low-Ti magnetite. Electron microprobe analyses show that the scapolite contains about 1.74 wt.% S, which indicates an atomic S/(S + C) of 0.58. Although scapolite occurs in xenoliths in volcanic rocks and diatremes, as well as a metamorphic mineral in granulites, its occurrence as a primary igneous mineral is extremely rare.
Ca-rich scapolite has been crystallized experimentally by others from melts with a wide range of SiO2, CaO, and Na2O contents, at temperatures above 825°C and pressures ranging from 3 to 15 kbar. Comparison of scapolite from this latite with synthetic scapolite crystallized from nepheline syenite melt suggests that the Arizona phenocrysts crystallized under conditions of 850 to 900°C, 3-6 kbar total pressure, and unusually high ƒ;CO2 and ƒ;SO2. The rarity of scapolite as a phenocryst mineral suggests that high partial pressures of CO2 and SO2 are rare in the magmatic environment.
Arney Barbara H.
Eddy Andrea C.
Goff Fraser
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