Magma evolution in the Stillwater complex, Montana: I. Rare-earth element evidence for the formation of the ultramafic series.

Abstract

Abundances and partitioning of trace elements in cumulus orthopyroxenes, as well as major-element compositions, indicate that multiple injection and fractional crystallization of magmas derived from the upper mantle were responsible for formation of the series. Dynamic partial melting may have been the principal genetic process. The partial melts may have been contaminated by LREE-enriched crustal rocks en route to the magma chamber. The mantle source region, however, may initially have been enriched in LREE. Extensive diagrammatic, tabulated and bibliographic data are presented.-M.S.