Geochemical and Nd-Pb isotopic systematics of late Archean granitoids, southwestern Slave Province, Canada: Constraints for granitoid origin and crustal isotopic structure

Katsuyuki Yamashita, Robert A. Creaser, James U. Stemler, Tony W. Zimaro

Research output: Contribution to journalArticlepeer-review

Abstract

New geochemical and Nd-Pb isotopic data for ~2.62-2.59 Ga granitoids from the southwest Slave Province are used to determine the source(s) of granitoid magmas, to evaluate the role of pre-2.8 Ga basement during this magmatism, and to refine the existing Nd-Pb isotopic structure of the western Slave Province. The Pb isotopic data require crust older than ~3.2 Ga as a granitoid protolith, whereas the Nd isotopic data require input from juvenile crustal material. This discrepancy is explained if the granitoid protoliths are mixtures of ancient basement and ~2.7 Ga juvenile crust in varying proportions. Specifically, granitoids from the southwestern Slave Province require 10-30% basement, whereas granitoids from other parts of the western Slave Province require >50%. Incorporation of basement as a protolith may be achieved indirectly, by assimilation of basement during juvenile ~2.7 Ga magmatism, or directly during ~2.62-2.59 Ga magmatism. The granitoid isotopic data suggest that indirect basement input was important on a regional scale, but direct input may have also taken place in some areas of the western Slave Province, particularly along the ~111°W 'isotopic boundary' zone previously recognized. The geochemical characteristics of these granitoids are compatible with an origin by partial melting of dominantly amphibolite and metasedimentary rocks to produce the ~2.61 Ga and ~2.59 Ga magmatism, respectively; partial melting occurred in response to regional crustal thickening at this time.

Original languageEnglish
Pages (from-to)1131-1147
Number of pages17
JournalCanadian Journal of Earth Sciences
Volume36
Issue number7
DOIs
Publication statusPublished - Jul 1999
Externally publishedYes

ASJC Scopus subject areas

  • Earth and Planetary Sciences(all)

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