Garnet-spinel-olivine-orthopyroxene equilibria in the FeO-MgO-Al2O3-SiO2-Cr2O3 system: I. Composition and molar volumes of minerals

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

“…This model shows good agreement with the available experimental data in both Cr-poor and Cr-rich mantle Compositions from LS1 to BN4 were taken from Stern et al (1999) and were normalized to 100 wt% after removing TiO compositions (e.g. Nickel 1986;Webb and Wood 1986;Walter 1998;Brey et al , 1999Brey et al , 2008 and is therefore considered to be more appropriate for an application to a set of natural mantle xenoliths such those from Pali-Aike (bulk Cr# = 0.05-0.30). We would like to caution the reader that the values reported as enthalpies of formation in Table 2 of Klemme et al (2009) and supplementary table of Ziberna et al (2013) are actually free energies of formation and that the Cr-bearing clinopyroxene end-member used in the calculations is CaCr 2 SiO 6 and not MgCr 2 SiO 6 .…”

“…, 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).…”

Major element composition of concentrate garnets in Proterozoic kimberlites from the Eastern Dharwar Craton, India: Implications on sub-continental lithospheric mantle

“…In Cr-bearing systems a pressure-temperature field exists where garnet and spinel coexist. The width of this divariant field strongly depends on the Cr/ (Cr + Al) of the system, and with increasing values of this ratio the spinel-garnet transition progressively shifts to pressures as high as $70 kbar (Brey et al, 1999;Klemme, 2004). The wide ranges of Cr/(Cr + Al) ratios of concentrate garnets from both the NKF and WKF (Fig.…”

Origins of orogenic dunites: Petrology, geochemistry, and implications

“…The Cr# of spinel in garnet peridotites is currently controlled by the spinel-garnet transition (SGT) reaction. With increasing pressure, Mg-Al spinel and orthopyroxene would first be transformed to pyrope and olivine, making the residual spinel enriched in Cr (Brey et al, 1999;Klemme, 2004). In the residual dunites, except for chromite or Cr-spinel, minerals enriched in chromium and/or aluminum (e.g., garnet) are extremely rare or absent.…”