Nickel upper mantle composition

Palme H. and Nickel K. G. (1985) Ca/Al ratio and composition of the Earth s upper mantle. Geochim. Cosmochim. Acta 49, 2123-2132. 

The superchondritic Mg/Si ratio of Earth s upper mantle might arise from olivine flotation in an early magma ocean (Agee and Walker, 1988). Such an explanation would have to be consistent with other minor and trace elements, especially those known to be compatible in olivine at low pressure such as nickel, cobalt, and manganese. Olivine is a stable liquidus phase in chondritic and peridotitic compositions to 15 GPa (Agee et aL, 1995 Zhang and Herzberg,... 

Temperature and pressure both increase with depth in the Earth and control the composition and properties of the material present at various depths. The Earth comprises a number of layers, the boundaries between which are marked by relatively abrupt compositional and density changes (Fig. 1.1). The inner core is an iron-nickel alloy, which is solid under the prevailing pressure and temperature ranges. In contrast, the outer core is molten and comprises an iron alloy, the convection currents within which are believed to drive the Earth s magnetic field. The core-mantle boundary lies at c. 2900km depth and marks the transition to rocky material above. The mantle can be divided into upper and lower parts, although the boundary is quite a broad transitional zone (c.lOOCM-OOkm depth). It behaves in a plastic, ductile fashion and supports convection cells. The upper mantle layer from c.100 to 400 km depth is called the asthenosphere, and its convection system carries the drifting continental plates. 

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