High temp geochem - trace element

Trace element

Element present in <0.1 wt% (1000 ppm) in rocks.

Major element

Element making up >1 wt% of a rock.

Minor element

Element present between 0.1–1 wt%.

Direct substitution

Trace element replaces a major element in a mineral’s structure due to similar size/charge.

Schottky defect

Vacancy created by atoms leaving their lattice sites.

Frenkel defect

Atom leaves its site and moves to an interstitial position.

Distribution coefficient (D)

Ratio of element concentration in solid to liquid: D = Cs / Cl.

Compatible element

Element with D > 1; prefers to stay in solid.

Incompatible element

Element with D < 1; prefers the melt.

Equilibrium melting

Melt remains in chemical equilibrium with residue; uses mass balance equations.

Fractional melting

Melt is removed as it forms; incompatible elements strongly concentrated in melt.

Equilibrium crystallisation

Crystals stay in contact with melt; composition adjusts continuously.

Fractional crystallisation

Crystals removed from melt; residual melt becomes enriched in incompatible elements.

Bulk distribution coefficient (D_bulk)

Weighted average D based on mineral proportions in a rock.

Spider diagram

Plot of trace element concentrations normalized to a reference to show mantle processes.

Partial melt (F)

Fraction of melt extracted from a solid rock during melting.