Phlogopite, stability

Wendlandt RF, Eggler DH (1980) The origins of potassic magmas 2. Stability of phlogopite in natural spinel Iherzolite and in the system KalSi04-Mg0-H20-C02 at high pressures and high temperatures. Am J Sci 280 421-458... 

Further experimental studies on the stability of the magnesian phlogopite component in silica undersaturated and oversaturated systems have been carried out by various authors. Wones (1967) investigated the equilibrium... 

Wood (1976a) studied the stability of phlogopite in the presence of quartz ... 

Figure 5,45 P-T stability curve of phlogopite compared with the incipient melting curves of granite and basalt. Reprinted from H. S. Yoder and H. R Eugster, Geochimica et Cos-mochimica Acta, 6, 157-185, copyright 1954, with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington 0X5 1GB, UK.

Figure 5.51 fo2 stability field of biotite. (A) Pseudobinary phlogopite-annite mixture. Numbers at experimental points indicate observed Fe/(Fe + Mg) atom ratio. (B) Annite. HM = hematite-magnetite buffer NNO = Ni-NiO buffer MW = magnetite-wuestite buffer QFM = quartz-fayalite-magnetite buffer. From Wones and Eugster (1965). Reprinted with permission of The Mineralogical Society of America. 

Wones D. R. (1967). A low pressure investigation of the stability of phlogopite. Geochim. Cos-mochim. Acta, 31 2248-2253. 

Wones D. R. and Dodge F. C. W. (1977). The stability of phlogopite in the presence of quartz and diopside. In Thermodynamics in Geology, D. G. Fraser, ed. Dordrecht-Holland, Reidel. 

Yoder H. S. and Eugster H. P. (1954). Phlogopite synthesis and stability range. Geochim. Cosmochim. Acta, 6 157-185. 

Two additional suites of mantle-derived samples found in kimberlites provide evidence for amphibole and/or mica stability in the lithospheric mantle. These are the ilmenite-rutile-phlogopite-sulphide (IRPS) and mica-amphibole-rutile-ilmenite -diopside (MARID)... 

Konzett and Ulmer (1999) bracketed the phlogopite-out reaction in a natural peridotite at 6-7 GPa at 1,150 °C and in a subalkaline iron-free bulk composition at 8-9 GPa at 1,150 °C and at <8 GPa at 1,200 °C (Figure 3). Phlogopite becomes unstable with increasing pressure relative to a potassium-rich amphibole the stability of this amphibole has been studied by a number of workers (Figure 3). 

Modreski and Boettcher (1973), Sudo and Tatsumi (1990) and Luth (1997) determined the stability of phlogopite coexisting with clinopyroxene (Figure 4). With increasing pressure, phlogopite breaks down to form a potassic amphibole, which in turn decomposes at higher pressure to form another hydrous potassium magnesium silicate, termed phase X by Trpnnes (1990). 

The general sequence of stability of hydrous phases with increasing pressure (phlogopite K-amphibole phase X) has been seen consistently in studies of various bulk compositions relevant to peridotites (Figure 3). The same sequence was also seen in studies of a peralkaline bulk composition (Figure 5), in which the stability fields of potassium-rich phases should be maximized (Konzett et ai, 1997 Konzett and Fei, 2000). 

The presence of apatite in subcontinental mantle samples raises the question of the thermal stability of apatite, and whether it would be stable in mantle other than cool lithospheric roots. A limited amount of experimental work has been done that addresses this question Vukadinovic and Edgar (1993) determined the solidus for phlogopite-apatite mixtures at 2 GPa in the KaO-CaO-MgO-AljOa-SiOa-PaOs-HjO-F system. They looked at two bulk compositions, one with the hydroxy end-members and the other where F/OH = 1. The sohdus was 1,225 °C for the fluorine-free system, and 1,260 °C for the fluorinebearing system. It seems likely that adding iron to the system will decrease solidus temperatures. Given that the average current mantle adiabat is... 

Trpnnes R. G. (2002) Stability range and decomposition of potassic richterite and phlogopite end members at 5-15 GPa. Mineral Petrol 74, 129-148. 

The mica group has about 30 members but only a few are common. Muscovite, phlogopite, and biotite are important representatives of this group. Muscovite is one of the most common of the micas and occurs in a wide variety of geological environments because of its stability. Crystals measuring 2-3 m across are mined in some locations. Muscovite can vary in chemical composition as a result of atomic substitution (Na for K Mg and F for Al). 

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