Granulite fades Nd-isotopic homogenization in the Lewisian complex of northwest Scotland

M.J. Whitehouse

doi:10.1038/331705a0

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Granulite fades Nd-isotopic homogenization in the Lewisian complex of northwest Scotland

M.J. Whitehouse

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Abstract

A published Sm–Nd whole-rock isochron of 2,920 ± 50 Myr, obtained from a wide range of lithologies in the Lewisian complex of north-west Scotland, was interpreted 1 as the time of protolith formation. This date is ∼ 260 Myr older than estimates for the timing of high-grade metamorphism in the complex at ∼ 2,660 Myr 2'3 , and this period is considered to represent the duration of the Lewisian crustal accretion-differentiation superevent (CADS) 4 . Here we give new Sm-Nd data, obtained specifically from granulite facies tonalitic gneisses, that yield a date of 2,600 ±155 Myr. Although depleted-mantle model ages ( t DM suggest >200 Myr of premetamorphic crustal residence, the regression date and its associated initial Nd-isotopic parameters demonstrate Nd-isotopic homogenization during the high-grade event, as well as the probability of general rare-earth-element (REE) mobility. Models for selective element depletion in the complex have previously assumed REE immobility since 2,920 Myr, but the data presented here suggest that a reappraisal of the depletion mechanism is required.

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Source-reported bounding extent: 56.07473135845302° to 58.5924285295051° latitude; -7.80190488310231° to -3.853372128121464° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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M.J. Whitehouse. 1988. Granulite fades Nd-isotopic homogenization in the Lewisian complex of northwest Scotland. https://doi.org/10.1038/331705a0

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