The behavior of lithium in amphibolite- to granulite-facies rocks of the Ivrea-Verbano Zone, NW Italy

To investigate the behavior of Li during high-grade metamorphism and the Li composition of the lower continental crust, the Li concentrations ([Li]) and isotopic compositions (delta Li-7) of amphibolite- to granulite-facies metapelites, leucosomes and metabasites from the Ivrea-Verbano Zone, NW, Italy were determined. The average [Li] of amphibolite facies kinzigites (79 +/- 69 mu g/g, 2 sigma) is higher than that of granulite facies stronalites (8 +/- 6 mu g/g, 2 sigma) that experienced partial melting via biotite dehydration reactions. Biotite abundance and the [Li] in metapelites correlate positively, reflecting the importance of Mg-bearing phyllosilicates in controlling the Li budget of the metapelites. Despite the loss of Li following biotite breakdown, there is no significant change in delta Li-7, which averages -1.4 +/- 2.0 (2 sigma, excluding an anomalously light sample) in the kinzigites (amphibolite facies) and +0.9 +/- 2.9 (2 sigma) in the stronalites (granulite facies). Both average delta Li-7 values are comparable with those of other pelitic sediments and likely reflect the delta Li-7 of their protoliths. An anomalous kinzigitic sample, with the lowest. delta Li-7 (-8.4) and the highest [Li] (120 mu g/g), has extremely low Ba and Sr concentrations and the highest CIA value, all indicators of a highly weathered protolith, which was likely isotopically light prior to significant metamorphism. This sample may also have experienced Li addition via diffusion, increasing [Li] and lowering ea The leucosomes in the kinzigites and stronalites are interpreted to have formed in different ways; the former precipitated from hydrothermal fluids, have an average [Li] = 13 +/- 2.6 mu g/g (2 sigma) and are isotopically similar to the kinzigites (delta Li-7 = -1.0 +/- 0.2, 2 sigma); the latter formed by dehydration melting and have lower [Li] (3 +/- 2.6 mu g/g, 2 sigma) that is heavier (delta Li-7 = + 6.0 +/- 6.3, 2 sigma) than that of the stronalites or kinzigites. The mineralogical and compositional characteristics of the stronalites are consistent with substantial Li loss during partial melting. A melting model indicates that Li removed from the stronalites may contribute to the formation of S-type granites or Li-enriched pegmatites. Three granulite-facies metabasites have relatively constant [Li] of 3.0-4.2 mu g (average 3.6 +/- 1.2, 2 sigma) and variable delta Li-7 of -3.2 to + 3.3 (average 0 +/- 6.5, 2 sigma). While these concentrations are typical of those of possible basaltic protoliths, the highly variable delta Li-7 suggests Li mobility during metamorphism. Collectively, the Li signatures in granulite facies stronalites and metabasites indicate the [Li] of this section of lower continental crust is close to 8 mu g/g or less, and the concentration weighted delta Li-7 of this section of the lower continental crust is + 1.0, which is similar to a previous estimate (8 mu g/g, + 2.5). Published by Elsevier B.V.