Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (13) Citing Articles via Google Scholar Google Scholar Articles by Schmitz, M. D. Articles by Patchett, P. J. Search for Related Content GeoRef GeoRef Citation

Decoupling of the Lu-Hf and Sm-Nd isotope systems during the evolution of granulitic lower crust beneath southern Africa

¹ Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, D.C. 20015, USA, and Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
² Department of Geology, Washington State University, Pullman, Washington 99164, USA, and Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA
³ Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
⁴ Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA

The Lu-Hf and Sm-Nd isotope systems in kimberlite-borne, Archean to Proterozoic lower-crustal granulite xenoliths from southern Africa display significant parent-daughter fractionations and corresponding isotopic anomalies resulting in the decoupling of these generally well correlated systems. Systematic compositional and mineralogical controls on decoupling have also been identified. Opposite senses of divergent evolution from the terrestrial Hf-Nd isotope array are demonstrated in mafic granulite samples versus felsic and metasedimentary granulite samples. The former have superchondritic Lu/Hf and ¹⁷⁶Hf/¹⁷⁷Hf ratios at subchondritic Sm/Nd and ¹⁴³Nd/¹⁴⁴Nd ratios, whereas the latter have subchondritic Lu/Hf and ¹⁷⁶Hf/¹⁷⁷Hf ratios at a wide range of subchondritic to superchondritic Sm/Nd and ¹⁴³Nd/¹⁴⁴Nd ratios. This decoupling is shown to be related to the mineralogical sensitivity of crustal protolith Lu/Hf ratios to fractionation upon anatexis in the presence not only of residual garnet and accessory zircon, but also the residual oxide minerals (rutile versus iron-titanium oxides). The isotope diversity observed in these deep-crustal melt residues supports suggestions that the Hf-Nd systematics of complementary crustal melts may be useful fingerprints for deciphering the mineral assemblage and geochemical character of granitoid magma sources, and that together these systematics can yield insights into the origin and differentiation of continental crust.

Key Words: Lu-Hf • Sm-Nd • U-Pb • lower crust • xenoliths • granulite • zircon • garnet • rutile

This article has been cited by other articles:

				H. Kitagawa, K. Kobayashi, A. Makishima, and E. Nakamura Multiple Pulses of the Mantle Plume: Evidence from Tertiary Icelandic Lavas J. Petrology, July 1, 2008; 49(7): 1365 - 1396. [Abstract] [Full Text] [PDF]

				T.S. Rohr, H. Austrheim, and M. Erambert Stress-induced redistribution of yttrium and heavy rare-earth elements (HREE) in garnet during high-grade polymetamorphism American Mineralogist, August 1, 2007; 92(8-9): 1276 - 1287. [Abstract] [Full Text] [PDF]

				P. E. JANNEY, A. P. LE ROEX, and R. W. CARLSON Hafnium Isotope and Trace Element Constraints on the Nature of Mantle Heterogeneity beneath the Central Southwest Indian Ridge (13{degrees}E to 47{degrees}E) J. Petrology, December 1, 2005; 46(12): 2427 - 2464. [Abstract] [Full Text] [PDF]