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Hf isotope systematics of kimberlites and their megacrysts : New constraints on their source regions.

Nowell, G. M. and Pearson, D. G. and Bell, D. R. and Carlson, R. W. and Smith, C. B. and Kempton, P. D. and Noble, S. R. (2004) 'Hf isotope systematics of kimberlites and their megacrysts : New constraints on their source regions.', Journal of petrology., 45 (8). pp. 1583-1612.


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 Hf values. Group I kimberlites have Hf 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 (Hf 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 (Hf values 3.6 to –2.6). The data indicate a genetic link between kimberlites and the low-Cr megacryst suite. The negative Hf 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.

Item Type:Article
Additional Information:
Keywords:isotopes; kimberlites; lutetium–hafnium; megacrysts.
Full text:Full text not available from this repository.
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Date accepted:No date available
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Date of first online publication:August 2004
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