Lithium Isotope Geochemistry

Abstract

The lithium isotope system is increasingly being applied to a variety of Earth science studies, as the burgeoning literature attests; over 180 papers have been published in the last twelve years that report lithium isotope data, including five review papers that cover different aspects of lithium isotope applications (Elliott et al. 2004; Tomascak 2004; Tang et al. 2007b; Burton and Vigier 2011; Schmitt et al. 2012), and a book (Tomascak et al. 2016). The upswing in lithium isotope studies over the past decade reflects analytical advances that have made Li measurements readily obtainable. These include the use of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) for relatively precise solution measurements (Tomascak et al. 1999a) and secondary ion mass spectrometry (SIMS) for high spatial resolution measurements (Chaussidon and Robert 1998; Kasemann et al. 2005; Bell et al. 2009). In addition, lithium isotope studies are motivated by the large variety of problems for which they may provide insight, including crust–mantle recycling, silicate weathering, fluid–rock interaction, as well as geospeedometry. The great interest in the Li system that spurred the development of these new analytical methods was initiated by the pioneering work of Lui-Heung Chan, who demonstrated not only that Li isotopic fractionation can be very large at or near the Earth’s surface (Chan and Edmond 1988), but also that Li isotopes are strongly fractionated during seawater-basalt interaction (Chan et al. 1992). This discovery naturally led to the search for a recycled slab signature in Li isotopes of arc lavas (some of the earlier studies include Moriguti and Nakamura 1998a; Chan et al. 1999, 2002b; Tomascak et al. 2000, 2002; Leeman et al. 2004; Moriguti et al. 2004), as well as more deeply derived intraplate basalts (e.g., Chan and Frey 2003 …