On the difficulty of assigning crustal residence, magmatic protolith and metamorphic ages to Lewisian granulites: Constraints from combined in situ U-Pb and Lu-Hf isotopes

M. J. Whitehouse, A. I.S. Kemp

Research output: Contribution to journalArticle

50 Citations (Scopus)

Abstract

Zircons from two granulite facies gneisses from the central region of the Lewisian Complex have been investigated by high spatial resolution ion-microprobe U-Pb dating and laser ablation combined Pb-Hf isotope methods. The ion-microprobe data reveal a complex pattern of zircon ages distributed along the concordia curve between the time of granulite facies metamorphism at c. 2.5 Ga and the oldest zircon in each sample (respectively 2.89 Ga and 3.04 Ga). This Pb-loss pattern complicates assignment of an unambiguous magmatic protolith age to the zircon although cathodoluminescence (CL) imaging is used to suggest a preferred age of c. 2.85 Ga for both samples, with older grains being inherited. In situ Hf isotopes show a larger spread in the sample containing older grains which is also consistent with inheritance and further suggests that several crust extraction events are represented in the inherited population. Comparison of Hf isotope compositions with plausible model evolution curves suggests that crustal precursors to the Lewisian granulites were derived from their mantle source at c. 3.05-3.2 Ga.

Original languageEnglish
Pages (from-to)81-101
Number of pages21
JournalGeological Society Special Publication
Volume335
DOIs
Publication statusPublished - 31 Aug 2010
Externally publishedYes

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