Geochemistry and origin of Archean volcanic rocks from the Upper Keewatin assemblage (ca 2.7 Ga), Lake of the Woods Greenstone Belt, Western Wabigoon Subprovince, Superior Province, Canada
Version of Record online: 22 FEB 2007
Volume 16, Issue 1, pages 191–208, March 2007
How to Cite
Ujike, O., Goodwin, A. M. and Shibata, T. (2007), Geochemistry and origin of Archean volcanic rocks from the Upper Keewatin assemblage (ca 2.7 Ga), Lake of the Woods Greenstone Belt, Western Wabigoon Subprovince, Superior Province, Canada. Island Arc, 16: 191–208. doi: 10.1111/j.1440-1738.2007.00566.x
- Issue online: 22 FEB 2007
- Version of Record online: 22 FEB 2007
- Received 4 October 2005; accepted for publication 26 October 2006.
- arc volcanism;
- greenstone belt;
- mantle plume;
- Nb-enriched basalts and andesites;
Abstract Volcanic rocks from the Upper Keewatin assemblage (ca 2720 Ma) were geochemically classified into five groups; komatiites, tholeiitic rocks having near-flat primitive mantle-normalized abundance patterns, Nb-enriched basalts and andesites (NEBA) plus normal calc-alkaline (NCA) rocks, adakites and shoshonites. The adakites having [La/Yb]N >30 and <30 were probably derived from felsic magmas formed by partial melting of a subducted slab at relatively greater and smaller depths, respectively. Ascending adakite magmas, by interaction with the overlying mantle wedge, decreased in Al2O3 / Y ratio and selectively lost high-field strength elements, thereby forming mantle sources for both NEBA + NCA and shoshonite magmas. Under the influence of a mantle plume, the source of komatiites, the NEBA + NCA magmas were generated from that part of the mantle wedge metasomatized by adakite magmas having [La / Yb]N <30, and tholeiitic magmas from unmetasomatized part of the same mantle wedge. Magmas of both adakites having [La / Yb]N >30 and shoshonites were generated in a normal Archean Arc system setting.