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TitleArchean high-Mg granodiorite: a derivative of light rare earth element-enriched monzodiorite of mantle origin
AuthorStern, R A; Hanson, G N
SourceJournal of Petrology vol. 32, pt. 1, 1991 p. 201-238,
Alt SeriesGeological Survey of Canada, Contribution Series 2000263
PublisherOxford University Press (OUP)
Mediapaper; on-line; digital
File formatpdf
NTS21E; 21L; 21M; 22D; 22E; 22L; 22M; 23D; 23E; 23L; 23M; 24D; 24E; 24L; 24M; 31; 32; 33; 34; 41; 42; 43; 44; 52; 53; 54; 62G; 62H; 62I; 62J; 62O; 62P; 63A; 63B; 63G; 63H; 63I; 63J; 63O; 63P; 64A; 64B; 64G; 64H; 64I; 64J; 64O; 64P
Lat/Long WENS-100.0000 -70.0000 60.0000 44.0000
Subjectsgeochemistry; geochronology; igneous and metamorphic petrology; mineralogy; structural geology; Archean; rare earths geochemistry; mantle; monzodiorites; granodiorites; diorites; minerals; igneous rocks
Illustrationslocation maps; geological sketch maps; ternary diagrams; tables; geochemical plots; graphs; cross-sections, structural; schematic diagrams
ProgramNSERC Natural Sciences and Engineering Research Council of Canada
AbstractThe Roaring River Complex, Superior Province, Canada, contains rocks varying from diorite and monzodiorite to granodiorite which are characterized by high mg-numbers (0.43-0.62), high abundances of Cr (0.80) with low Rb/Sr ratios (<0.02) and light-REE enrichment relative to chondrites. The differences in the REE patterns of monzodiorite samples do not support, nor rule out, garnet in the residue for melting. If the monzodioritic melts were derivatives of other melts, the parent melts would have been similar to high-Mg monzodiorites ('sanukitoids') recognized as components of other diorite-granodiorite bodies in the region. An Rb-Sr whole-rock isochron (n = 25) yields a minimum crystallization age of 2623 Ma (+/-19) with initial 87Sr/86Sr = 070134 (000004; MSWD=l.8). Sm-Nd isotope data for six rocks yield ϵ Nd (2623)= +0.8 0.3. The isotope data indicate a source region with long-term Rb/Sr of ?0.02, similar to depleted mantle, and light-REE depletion relative to chondrites. The peridotite source to the diorite-granodiorite series became light-REE enriched before melting through the addition of a light-REE component of a fluid or melt. In generating Archean granodiorite with suitably high mg-numbers, and Ni, Cr, Sr, Ba, P2O5, and light-REE contents, these data indicate: (1) the importance of crystallization differentiation of high-Mg monzodioritic parent magmas, (2) that the steep REE patterns may be a characteristic of the source rocks, and (3) light-REE-enriched, peridotitic sources were melting and contributing siliceous material directly to the Archean crust.

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