Assimilation and fractional crystallization

DePaolo, D. J. (1981). Trace-element and isotopic effects of combined wallrock assimilation and fractional crystallization. Earth Planet. Sci. Letters, 53, 189-202. 

Mantovani, M. S. M. Hawkesworth, C. J. (1990). An inversion approach to assimilation and fractional crystallization processes. Contr. Mineral. Petrol., 105, 289-302. 

Spera, F.J. and Bohrson, W.A., 2001. Energy-constrained open-system magmatic processes I general model and energy-constrained assimilation and fractional crystallization (EC-AFC) formulation. J. Petrol., 42 999-1018. 

Barker DS (1987) Rhyolites contaminated with metapelite and gabbro, Lipari, Aeolian Islands, Italy products of lower crustal fusion or of assimilation plus fractional crystallization Contrib Mineral Petrol 97 460-472... 

If phenocryst compositions cannot explain trends in a rock series and a fractional and/racttonal crystallization model does not. appear to worlt, it is instructive to consider the crystallization possibility of simultaneous assimilation, of the country rock and fractional crystallization. This process, often abreviated to AFC, was first proposed by Bowen... 

Plot of Sr/ Sr ratio vs 5 0 showing the trajectories that would be followed during assinuladon and fractional crYStallization in a magma chamber. The initial composition of the melt is Sr/ Sr = 0.703, S 0 = 5.7, The two sets of curves represent two different ratios of Sr in the melt to Sr in the assimilated country rodt. The solid lines represent a melccountry rock ratio of 10 1 and the dashed lines a ratio of 5 1, The ratio of cumulates to assimilated country rock is 5 1. Higher values produce curves with lower S O values. 0 is the ratio of Sr in the cumulates to Sr in the melt, t.e. the bulk partition coeflicient of the cumulates. The end-points are placed at 99 % fractional crystallization. (Adapted from Taylor, 1980.)... 

The symbols used in Section 1.5 to describe the evolution of element i concentration in the solid and the liquid during fractional crystallization will be kept. Other parameters used in the present derivation are almost identical to those of DePaolo (1981) although reference to time, which is immaterial to the mass balance and equilibrium conditions, has been omitted. Let a be the subscript representing the assimilated material, and assume that country-rocks concentration Cj is constant. Mass balance requires... 

A key problem in the present natural analogue study is the distinction between chemical variations related to trace element migration during basalt alteration and variations due to magmatic fractionation and other syn-intrusive processes. The detailed evaluation of the available data has shown that the chemical and isotopic composition of the HC1 residues is largely controlled by fractional crystallization and syn-intrusive assimilation of salt. In contrast, the chemical composition of the leachates is strongly modified by post-intrusive alteration (Steinmann et al. 1999). 

Harris C, Smith HS, le Roex AP (2000) Oxygen isotope composition of phenocrysts from Tristan da Cunha and Gough Island lavas variation with fractional crystallization and evidence for assimilation. Contrib Mineral Petrol 138 164-175... 

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