In situ origin of platinum-group element-rich chromitite seams of the Rum Eastern Layered Intrusion,Scotland
The platinum-group element (PGE)-rich sulphide mineralization of the Rum Eastern Layered Intrusion is associated with laterally extensive 2 mm-thick chromitite seams that occur at the bases of several of the 16 cyclic mafic-ultramafic units that make up the intrusion.The chromitite seams are commonly developed along the edges of steeply inclined culminations and depressions at unit boundaries,even where these are vertically-oriented or overhanging.This is taken to indicate formation of the seams by in situ growth at a crystal mush-liquid interface.From the base towards the top,chromitite seams show systematic compositional trends,with the most primitive compositions occurring at their bases.The preservation of such delicate chemical zoning rules out a large-scale upward migration of interstitial melt from the underlying cumulate pile.The following sequence of events may explain the origin of the PGE-enriched chromitite seams: (a) emplacement of chromite-saturated picritic magma that caused thermal and mechanical erosion of underlying cumulates and gave rise to in situ growth of chromite against the base,(b) precipitation of sulphides in the immediate vicinity of the crystallizing chromite triggered by a decrease in the solubility of sulphur in the silicate melt and (c) effective scavenging of PGE by the sulphides from a continuous through-flow of fresh magma at the base of the intrusion.
R.Latypov B.O’Driscoll
Department of Geosciences,University of Oulu,Linnanmaa,90014,Finland School of Physical and Geographical Sciences,Keele University,Keele,ST5 5BG,UK
国际会议
贵阳
英文
93-96
2012-06-16（万方平台首次上网日期，不代表论文的发表时间）