Serpentinisation of harzburgites from the alpine peridotite belt of Southwest Turkey

Abstract

Analyses are presented for some harzburgites from southwest Turkey. These ultramafics, classed broadly as peridotites, show wide variation in the degree of alteration from fresh to fully serpentinised. A technique is described to recast the analyses into a realistic “normative” mineralogy. When the harzburgite analyses are recalculated on a water-free basis the chemistry remains constant throughout the range of serpentinisation except for losses in respect of some minor constituents, notably Al 2O 3 and CaO, in fully serpentinised rocks. A simple equation representing isochemical (except for hydration) serpentinisation of harzburgite indicates a maximum expansion of approximately 39% of the original volume in the process of serpentinisation. This value is higher than those based upon specific gravity calculations using the normative mineralogy, or those depending on measured sample densities which are of the order of 25–30% of the original volume.