Crystallization of apatite in natural magmas under high pressure, hydrous conditions, with particular reference to 'Orogenic' rock series

T. H. Green*, E. B. Watson

*Corresponding author for this work

Research output: Contribution to journalArticle

176 Citations (Scopus)

Abstract

Two separate series of hydrous experiments involving (1) imposing apatite saturation on a series of igneous rock compositions from basanite to rhyolite, and (2) crystallizing similar natural rock compositions progressively until apatite appears, demonstrate a close dependence between apatite saturation and silica content of the magma, and determine P2O5 levels at a given silica value and temperature at which that composition may be expected to crystallize apatite. The effect of pressure on apatite solubility is not great, and is most significant for silicic compositions. P2O5 vs SiO2 relationships of the low-K island arc suite, calcalkaline suite and high-K calc-alkaline suite, appear regular and characteristic for each suite, and when linked with the experimental work on apatite solubility, indicate the following: (1) the low-K and calc-alkaline series have low P2O5 contents (∼0.1-0.2 wt.%) and relatively flat P2O5-SiO2 patterns; they do not show evidence of reaching apatite saturation until rhyodacite-rhyolite compositions are obtained for the low-K suite, and andesite-dacite compositions for the calc-alkaline suite; (2) the high-K calc-alkaline series has higher P2O5 contents (∼0.4-0.6 wt.%) in mafic compositions, and achieves apatite saturation over a wide compositional range for the series; (3) the calc-alkaline and high-K calc-alkaline series are probably lower temperature, and more hydrous than the low-K series; (4) anomalous P2O5-SiO2 distributions may indicate non-equilibrium crystallization of apatite, magma-mixing and crystal accumulation processes active in generation of the 'orogenic' volcanic series.

Original languageEnglish
Pages (from-to)96-105
Number of pages10
JournalContributions to Mineralogy and Petrology
Volume79
Issue number1
DOIs
Publication statusPublished - Apr 1982

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