Lherzolite xenoliths in kimberlites and basalts: petrogenetic and crystallochemical significance of some minor and trace elements in olivine, pyroxenes, garnet and spinel.

Electron and ion microprobe analyses for P, Si, Ti, Al, Cr, V, Sc, Fe, Mn, Mg, Ni, Co, Ca, Sr, Na, K and Li in olivine, pyroxene and garnet in 42 'cold' (<1150oC on the basis of two-pyroxene geothermometry) and 12 'hot' (>1150oC) garnet lherzolites from kimberlites, 9 spinel lherzolites from kimberlites and 18 from alkali basalts, and one 'cold' garnet lherzolite from the Malaita alnoite, are compared with published data for minerals occurring in lherzolite, harzburgite and eclogite xenoliths, for silicate megacrysts in kimberlites, and for silicate inclusions in diamonds. There are distinct regions in composition space that would enable determination of the parent lithology of disaggregated minerals in kimberlites and alkali basalts. Ti correlates with Fe³⁺ in garnets; Cr, Al, V and Sc are distributed similarly between silicates in lherzolites; Na correlates with trivalent ions in olivine, and increases with T; Na distribution (but not K and Li) between olivine and clinopyroxene correlates with T. Above the stability T of mica, 'metasomatizing fluids' may scavenge Cr and other trivalent ions as they increase Ti in silicates. -I.P.