Isotopic evidence from the eastern Canadian shield for geochemical discontinuity in the proterozoic mantle
Nature
By: L.D. Ashwal and J. L. Wooden
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Abstract
Most workers agree that Proterozoic anorthosite massifs represent the crystallization products of mantle-derived magmas1,2, although the composition of the parental melts is a major unsolved petrological problem 3. As mantle-derived rocks, the massifs can be used as geochemical probes of their late Precambrian upper mantle sources. We report here Nd and Sr isotopic compositions of anorthosites and related rocks from the Grenville and Nain Provinces of the eastern Canadian shield. Here 75% of the Earth's known anorthosite is found in a 1,600-km belt from the Adirondack Mountains of northern New York State to the eastern coast of Labrador4 (Fig. 1). The results indicate that the massifs were derived from at least two distinct mantle source regions which were established before 1,650 Myr ago, and were episodically involved in magmatism over ???500 Myr. One reservoir, below the Grenville Province, and probably below much of the eastern Superior Province, was isotopically similar to the depleted, modern-day mid-ocean ridge basalt (MORB) source. The other reservoir was chondritic to moderately enriched, and is most easily identified in the Nain Province, but may have occurred scattered throughout the Superior Province. ?? 1983 Nature Publishing Group.
Suggested Citation
Ashwal, L., Wooden, J.L., 1983, Isotopic evidence from the eastern Canadian shield for geochemical discontinuity in the proterozoic mantle: Nature, v. 306, no. 5944, p. 679-680, https://doi.org/10.1038/306679a0.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Isotopic evidence from the eastern Canadian shield for geochemical discontinuity in the proterozoic mantle |
| Series title | Nature |
| DOI | 10.1038/306679a0 |
| Volume | 306 |
| Issue | 5944 |
| Year Published | 1983 |
| Language | English |
| Larger Work Type | Article |
| Larger Work Subtype | Journal Article |
| Larger Work Title | Nature |
| First page | 679 |
| Last page | 680 |