Hf Isotope Systematics of Kimberlites and their Megacrysts: New Constraints on their Source Regions.
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| Title: | Hf Isotope Systematics of Kimberlites and their Megacrysts: New Constraints on their Source Regions. |
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| Authors: | NOWELL, G. M.1 g.m.nowell@durham.ac.uk, PEARSON, D. G.1, BELL, D. R.2, CARLSON, R. W.3, SMITH, C. B.4, KEMPTON, P. D.5, NOBLE, S. R.5 |
| Source: | Journal of Petrology. Aug2004, Vol. 45 Issue 8, p1583-1612. 30p. |
| Subjects: | Kimberlite, Basalt, Igneous rocks, Regolith, Petrology |
| Geographic Terms: | South Africa |
| Abstract: | Kimberlites from Southern Africa, along with their low-Cr megacrysts, have unusual Hf–Nd isotopic characteristics. Group I and Transitional kimberlites define arrays trending oblique to, and well below, the Nd–Hf isotope ‘mantle array’, defined by oceanic basalts, i.e. they have negative ΔɛHf values. Group I kimberlites have ΔɛHf values varying from −1.2 to −10.1. Low-Cr megacryst suites from individual Group I kimberlites have compositions that overlap those of their host kimberlites. The trend for all Group I kimberlite megacrysts (ΔɛHf values −1.0 to −9.0) shows a striking correspondence to that of the Group I kimberlite field. Group II kimberlites and their low-Cr megacrysts plot on or close to the mantle Nd–Hf array (ΔɛHf values 3.6 to −2.6). The data indicate a genetic link between kimberlites and the low-Cr megacryst suite. The negative ΔɛHf characteristics of Group I kimberlites and their megacrysts require a source component that is ancient (>1 Ga), and has evolved with low time-integrated Lu/Hf relative to Sm/Nd. Our preferred option is that this component originates beneath the lithosphere, from a reservoir of ancient, deeply subducted oceanic basalt that became incorporated into the convecting mantle source region for Group I and Transitional kimberlites. [ABSTRACT FROM AUTHOR] |
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| Database: | Engineering Source |
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