A new thermodynamic model for clino‐ and orthoamphiboles in the system Na₂O–CaO–FeO–MgO–Al₂O₃–SiO₂–H₂O–O

Abstract

A recent thermodynamic model for the Na-Ca clinoamphiboles in the system Na 2 O-CaO-FeO-MgOAl 2 O 3 -SiO 2 -H 2 O-O (NCFMASHO), is improved, and extended to include cummingtonite-grunerite and the orthoamphiboles, anthophyllite and gedrite. The clinoamphibole model in NCMASH is adopted, but the extension into the FeO-and Fe 2 O 3 -bearing systems is revised to provide thermodynamic consistency and better agreement with natural assemblage data. The new model involves order-disorder of Fe-Mg between the M2, M13 and M4 sites in the amphibole structure, calibrated using the experimental data on site distributions in cummingtonite-grunerite. In the independent set of end-members used to represent the thermodynamics, grunerite (rather than ferroactinolite) is used for FeO, with two ordered Fe-Mg end-members, and magnesioriebeckite (rather than ferritschermakite) is used for Fe 2 O 3 . Natural assemblage data for coexisting clinoamphiboles are used to constrain the interaction energies between the various amphibole end-members. For orthamphibole, the assumption is made that the site distributions and the non-ideal formulation is the same as for clinoamphibole. The data set end-members anthophyllite, ferroanthophyllite and gedrite, are used; for the others, they are based on the clinoamphibole end-members, with the necessary adjustments to their enthalpies constrained by natural assemblage data for coexisting clino-and orthoamphiboles. The efficacy of the models is illustrated with P-T grids and various pseudosections, with a particular emphasis on the prediction of mineral assemblages in ferric-bearing systems.

Petrology and possible significance of barroisite–bearing metabasite from the Kebara Formation in NW Kii Peninsula

“…4). Thermodynamic models of Ep and Chl are after Holland and Powell (1998), and that of amphibole after Diener et al (2007). Ab and Qz are considered as pure phases.…”

Hydrothermal spinel, corundum and diaspore in lower oceanic crustal troctolites from the Hess Deep Rift

“…6.6.8 (Connolly 2005(Connolly , 2009updated 2013) with the dataset of Powell (1998, updated 2002) and the CORK equation of state of fluids Powell 1991, 1998). Adopted solution models were Diener et al, (2007) for clinoamphibole, for olivine and spinel, Holland and Powell (1996) for orthopyroxene and clinopyroxene, for chlorite, and Holland and Powell (2003) for plagioclase.…”

Conflicting P–T paths within the Central Zone of the Limpopo Belt: A consequence of different thermobarometric methods?

“…Numerous workers have demonstrated that is it an extremely powerful and useful method for providing detailed P-T-X information for a variety of metamorphic environments (e.g. Powell et al, 1998;Vance and Mahar, 1998;White et al, 2001;Cononolly and Petrini, 2002;White et al, 2003;Zeh et al, 2004;Harris et al, 2004;White et al, 2004;Evans, 2004;Johnson and Brown, 2004;Pelletier et al, 2005;White et al, 2005;Kelsey et al, 2005;Stipska and Powell, 2005;Zeh et al 2005a,b;Konrad-Schmolke et al, 2006;Tenczer et al, 2006;Dziggel et al, 2006;White et al, 2007;Diener et al, 2007;Powell and Holland, 2008;White et al, 2008;Millonig et al, 2008;Diener et al, 2008;Kelsey et al, 2008;Mahan et al, 2008). A recent paper by Powell and Holland (2008) discusses at the length the advantages and disadvantages of a pseudosection approach in comparison to a conventional thermobarometric approach.…”