Lead isotopic study of early Proterozoic Wopmay Orogen, NW Canada: Role of continental crust in arc magmatism

Journal Article · Wed Nov 01 00:00:00 EST 1989 · Journal of Geology; (USA)

DOI:https://doi.org/10.1086/629355· OSTI ID:6852435

Housh, T; Bowring, S A; Villeneuve, M ^[1]

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1. Washington Univ., St. Louis, MO (USA)

Lead isotopes are sensitive indicators of crustal interaction in arc magmatism because of the large contrast in lead concentration between mantle-derived magmas and continental crust and the three independent decay paths in the U-Th-Pb system. Preserved within Wopmay Orogen (1.94 to 1.84 Ga) are the remnants of three magmatic arcs. The isotopic composition of lead in alkali feldspars separated from a diverse suite of samples from all three arcs fall in a relatively tight cluster with {sup 206}Pb/{sup 204}Pb = 15.59-15.88, {sup 207}Pb/{sup 204}Pb = 15.27-15.36, and {sup 208}Pb/{sup 204}Pb = 35.15-35.54, except for samples from the only plutonic suite within Wopmay Orogen observed to intrude Archean crust. Plutons intruding Archean crust have {sup 206}Pb/{sup 204}Pb = 15.29-15.49, {sup 207}Pb/{sup 204}Pb = 15.23-15.31, and {sup 208}Pb/{sup 204}Pb = 35.21-35.30. Lead isotopic compositions do not correlate with rock composition: both diorites and peraluminous granites have the same lead isotopic composition. This isotopic composition is elevated in {sup 207}Pb/{sup 204}Pb relative to mantle values at 1,870 Ma, suggesting that the lead isotopic signature of these magmas was dominated by a crustal reservoir. The extreme homogeneity of lead isotopes within Wopmay Orogen relative to those available in the Archean Slave Craton at 1.9 Ga preclude extensive involvement of Slave Craton in Wopmay magmatism, but it is consistent with involvement of only slightly older crust (ca. 2.0-2.4 Ga) whose presence has been inferred in the west. The involvement of only slightly older crustal material in arc magmatism may be considered an alternative to models invoking sediment subduction.

• OSTI ID: 6852435
• Journal Information: Journal of Geology; (USA), Vol. 97:6; ISSN 0022-1376
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CANADA
GEOLOGIC DEPOSITS
GEOLOGIC HISTORY
MAGMATISM
AGE ESTIMATION
CONTINENTAL CRUST
EARTH MANTLE
FELDSPARS
GEOLOGIC MODELS
ISOTOPE DATING
ISOTOPE RATIO
LEAD
LEAD 204
LEAD 206
LEAD 207
LEAD 208
MAGMA
MOUNTAINS
THORIUM
URANIUM
VARIATIONS
ACTINIDES
ALPHA DECAY RADIOISOTOPES
EARTH CRUST
ELEMENTS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
HEAVY NUCLEI
HOURS LIVING RADIOISOTOPES
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
LEAD ISOTOPES
METALS
MINERALS
NORTH AMERICA
NUCLEI
RADIOISOTOPES
SECONDS LIVING RADIOISOTOPES
STABLE ISOTOPES
YEARS LIVING RADIOISOTOPES
580000* - Geosciences