Geochemistry of the Dubois greenstone succession

An early Proterozoic bimodal volcanic association in west-central Colorado

Kent C. Condie*, Janet A. Nuter

*Corresponding author for this work

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

The Dubois greenstone succession, an Early Proterozoic supracrustal succession in west-central Colorado, is composed of fine-grained felsic volcaniclastic sediments, ash-flow tuffs, and tholeiitic flows, sills and dikes. The volcanic rocks comprise a bimodal suite of tholeiite and rhyolite. The tholeiites are divided into two groups: Group I exhibiting nearly flat REE patterns (20-30 × chondrites) and Group II with light REE-enriched patterns (40-70 × chondrites). These groups can be produced by two-stage melting of an undepleted or enriched garnet lherzolite source in which garnet remains in the residue of only the first melting stage which produces Group II magmas. The felsic magmas can be produced by partial melting of a high-grade gneiss in the lower crust in which zircon is entrained in the magma. The Dubois greenstone succession appears to have formed by felsic and mafic subaqueous eruptions in which some ash-flows, upon entering water, underwent phreatomagmatic explosions giving rise to detritus which formed the volcaniclastic sediments. Although tectonic setting cannot be assigned to the succession with a high degree of confidence, an immature back-arc basin developed on sialic crust in consistent with most data.

Original languageEnglish
Pages (from-to)131-155
Number of pages25
JournalPrecambrian Research
Volume15
Issue number2
DOIs
Publication statusPublished - 1981
Externally publishedYes

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