Phase relations of titan-phlogopite,K2Mg4TiAl2Si6O20(OH)4: a refractory phase in the upper mantle? |
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| Authors: | WC Forbes MFJ Flower |
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| Institution: | Department of Geological Sciences, University of Illinois at Chicago Circle, Chicago, Ill. USA;Institut für Mineralogie, Ruhr-Universität Bochum, Bochum Querenburg West Germany |
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| Abstract: | Experimental data on the stability of titan-phlogopite K2Mg4TiAl2Si6O20(OH)4] are presented which show it to be stable to substantially higher temperatures than normal phlogopite K2Mg6Al2Si6O20(OH)4]. A qualitative model to explain the role of titan-phlogopite during magma generation is put forward. Breakdown of titan-phlogopite during melting at depth (> 150km) on subducted lithospheric slabs is believed responsible for the concomitant increase of K and Ti observed in magmas erupted during orogenic volcanism. At lower pressures (up to about 10 kbar) beneath mid-oceanic ridges, titan-phlogopite is predicted to behave as a refractory phase during partial melting in the mantle, especially if H2O-excess conditions pertain, although at higher pressures in this environment it would almost certainly behave as a low-melting component. |
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