Sedimentary input to the source of Lesser Antilles lavas: A Li perspective Ming Tang a,⇑ , Roberta L. Rudnick a , Catherine Chauvel b,c a Department of Geology, University of Maryland, College Park, MD 20742, USA b Universite ´ Grenoble Alpes, ISTerre, F-38041 Grenoble, France c CNRS, ISTerre, F-38041 Grenoble, France Received 7 May 2014; accepted in revised form 1 September 2014; Available online 16 September 2014 Abstract Li isotopes in compositionally diverse Martinique lavas, as well as sea floor sediments cored at the southern (DSDP Site 144) and northern part (DSDP Site 543) of the subducting slab were analyzed in order to investigate the origin of the con- tinental crust compositional signature seen in Lesser Antilles lavas and to investigate Li cycling in arcs. Although the subduct- ing sediments display marked mineralogical and chemical shifts from south to north, the concentration-weighted mean d 7 Li for sediments from the two cores are indiscernible from each other (bulk d 7 Li = 0.5 ± 1.8, 1r, n = 15, d 7 Li = 4.4 to +2.9). This is the lowest bulk d 7 Li seen in subducting sediments from any trenches, and is significantly lower than that of MORB (d 7 Li  +4 ± 1). These low d 7 Li values reflect the dominance of terrigenous input and the influence of chemical weathering in the sediment’s continental provenance. With a few exceptions, the Li isotopic compositions of the Martinique lavas are also systematically lighter than MORB, yielding an average d 7 Li of +1.8 ± 1.3 (1r, n = 24, excluding three outliers that are iso- topically heavy, erupted below seawater and may have incorporated sea water Li). The d 7 Li values in the lavas show no cor- relation with most radiogenic isotope ratios ( 87 Sr/ 86 Sr, 143 Nd/ 144 Nd and 176 Hf/ 177 Hf), Li/Y, La/Sm or SiO 2 . There is also no correlation between d 7 Li and radiogenic isotopes in the subducting sea floor sediments. Thus, the low d 7 Li in the Martinique lavas likely reflects a mantle source that incorporated isotopically light subducted sediments. A two-end-member mixing mod- el requires sedimentary input of <1% to 5% by mass to a depleted mantle source to reproduce the Li isotopic compositions of the mafic samples, consistent with the range of sediment input (0.1–5%) inferred from radiogenic isotope data. The Lesser Antilles is the first arc shown to have d 7 Li systematically lower than MORB, reflecting the influence of subducted terrigenous sediments. Our data suggest that the enrichment of Li in most arc lavas is due to the addition of subducted sediment-derived Li, and that the isotopic signature of this Li can traverse the mantle wedge with little modification. It is only in arcs such as the Lesser Antilles where the Li isotopic composition of subducted sediments is very different from MORB that the slab signature is apparent in the lavas. Published by Elsevier Ltd. 1. INTRODUCTION Crustal materials are recycled to the mantle and juvenile arc crust is generated via arc magmatism above subduction zones. Arc lavas are chemically distinct from mid-ocean ridge basalts (MORB), in part due to incorporation of sub- ducted continental and oceanic crustal components in their source regions (Ryan and Chauvel, 2014, and references therein). Understanding the origin of crustal signatures in arc lavas provides insights into the mass exchange and recy- cling processes in subduction zones. Lithium isotopes are potentially useful tracers of recy- cling in subduction zones as they are readily fractionated at the Earth’s surface because of the relatively large mass http://dx.doi.org/10.1016/j.gca.2014.09.003 0016-7037/Published by Elsevier Ltd. ⇑ Corresponding author. Tel.: +1 2403743443; fax: +1 (301) 405 3597. E-mail address: tangmyes@gmail.com (M. Tang). www.elsevier.com/locate/gca Available online at www.sciencedirect.com ScienceDirect Geochimica et Cosmochimica Acta 144 (2014) 43–58