Lithium abundance and lithium isotope variations in mantle sources: insights from intraplate volcanic rocks from Ross Island and Marie Byrd Land (Antarctica) and other oceanic islands Jeffrey G. Ryan a,b, * , Philip R. Kyle c a Department of Geology, University of South Florida, 4202 East Fowler Avenue, Tampa, FL 33620, United States b Department of Terrestrial Magnetism, 4251 Broad Branch Road, NW, Washington, DC 20015, United States c Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, NM 87801, United States Received 4 April 2004; received in revised form 12 May 2004 Abstract The Li abundances and isotopic compositions of lavas from the McMurdo Volcanic Group (MVG) and the Crary Mountains, Antarctica and selected oceanic islands show Li is sensitive to both the mantle sources of basalts, and the open-system processes that occur during magmatic differentiation. Basaltic MVG lavas have uniform Li isotopic signatures, whereas more evolved lavas have variable y 7 Li indicating inputs of altered crustal materials. MVG basalts and those of the Crary Mountains have similar y 7 Li, and have compositions broadly consistent with mixing between a MORB-source mantle reservoir and a probable HIMU reservoir with elevated y 7 Li. y 7 Li values in ocean island basalt (OIB) samples examined range from +3x to +7x; only two ocean islands were distinguishable from MORBs. None of our OIB samples showed the anomalously low y 7 Li that Nishio et al. (2004) have contended is indicative of the EM1 mantle reservoir. Mixing of plume material with a MORB-like upper mantle can serve to mask extreme Li isotopic signatures to a degree, but it may also be the case that the mantle is heterogeneous in y 7 Li on the fine scales represented by xenolith hand samples, but relatively homogeneous on the scales of hotspot melting anomalies. D 2004 Elsevier B.V. All rights reserved. Keywords: Lithium abundance; Lithium isotope variation; Mantle; Ross Island; Marie Byrd Land 1. Introduction The radiogenic isotopic signatures of basaltic intraplate volcanic rocks have demonstrated the existence of chemical heterogeneities in the Earth’s 0009-2541/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.chemgeo.2004.08.006 * Corresponding author. Present address: Division of Under- graduate Education, National Science Foundation 4201 Wilson Boulevard, Arlington, VA 22230, United States. Chemical Geology 212 (2004) 125 – 142 www.elsevier.com/locate/chemgeo