Experimental constraints on phlogopite chemistry in lamproites

2. Effect of pressure-temperature variations

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Abstract

The chemistry of micas from high-pressure (5-40 kbar) experiments on leucite lamproite and olivine lamproite show much less variation as a function of pressure and temperature at fixed fluid composition in comparison to the variation due to fluid composition. Micas at high pressures tend to have higher Al2O3 and lower TiO2, K/Al and Cr2O3. Decreasing temperature produces decreasing Mg/(Mg + Fe) and Al2O3, and increasing SiO2, K2O and F in micas, but these trends may be a function of the degree of crystallization and may differ in natural lamproites where fractional crystallization occurs. Mica has higher TiO2 where it coexists with titanate minerals. Strongly olivine-normative lamproitic melts are likely agents of mantle enrichment in the sub-continental mantle at depths of 100-200 km. The sub-liquidus experimental mica compositions can be used to constrain models of vein chemistry in inhomogeneous mantle compositions. -from Author

Original languageEnglish
Pages (from-to)327-341
Number of pages15
JournalEuropean Journal of Mineralogy
Volume2
Issue number3
Publication statusPublished - 1990
Externally publishedYes

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