The Stability of Plagioclase in the Upper Mantle: Subsolidus Experiments on Fertile and Depleted Lherzolite

Partial melting of secondary pyroxenite at 1 and 1.5 GPa, and its role in upwelling heterogeneous mantle

“…Both M5-40 and M5-103 have plagioclase in the subsolidus assemblage at 1 GPa, 30 and 4%, respectively, whereas plagioclase is not stable in GV10 pyroxenite. This is due to the much lower Na 2 O/CaO ratio of GV10, which tends to stabilize plagioclase at lower pressure (Green and Falloon 1998;Borghini et al 2010). Spinel is present in very low modal abundance (<1%) or absent in the experiments on M5-40 and M5-103.…”

Volcanology and geochemical study of the volcanic rocks of the Bafmeng area (Mount Oku, Cameroon Volcanic Line)

“…Melt pockets together with their associated minerals are likely subsequent manifestation hence, rehomogenisation stage (Tamen et al, 2015). Therefore, the transition of spinel to plagioclase lherzolite in the mantle xenoliths of Bafmeng is governed by a continuous reaction resulting in a systematic compositional variation in coexisting minerals at decreasing pressure within the plagioclase stability field (Borghini et al, 2010). The development of a plagioclase bearing assemblage indicates that this peridotite have been partially reequilibrated at relatively low pressure, from spinel to plagioclase lherzolite facies condition (Rampone et al, 1995) and it turns out that, this type of peridotite at the initial state was at equilibrium at the spinel facies, but underwent a destabilisation and after re-equilibrium in the plagioclase facies (Tamen et al, 2015).…”

Application of thermodynamic modelling to natural mantle xenoliths: examples of density variations and pressure–temperature evolution of the lithospheric mantle

“…, have a strong effect of phase relations (O'Neill 1981;Nickel 1986;Webb and Wood 1986;Brey et al 1999;Girnis and Brey 1999;Klemme and O'Neill 2000a;Klemme 2004;Borghini et al 2009;Klemme et al 2009). While Cr (and other minor elements) probably does not affect phase relations in the deeper upper or the lower mantle much, Cr is known to partition very unevenly between upper mantle mineral phases and it is well known to strongly stabilize spinel relative to garnet (O'Neill 1981;Asimow et al 1995;Klemme 2004).…”

“…Therefore, experiments in complex compositions are especially difficult to conduct and experimental results are often difficult to interpret (e.g. Green and Ringwood 1967;Brey et al 1999;Girnis and Brey 1999;Girnis et al 2003;Borghini et al 2009;Fumagalli et al 2014).…”