Lithium isotopic systematics of peridotite xenoliths from Hannuoba, North China Craton: Implications for melt-rock interaction in the considerably thinned lithospheric mantle

Yan Jie Tang, Hong Fu Zhang, Eizo Nakamura, Takuya Moriguti, Katsura Kobayashi, Ji Feng Ying

Research output: Contribution to journalArticle

108 Citations (Scopus)

Abstract

Li concentrations and isotopic compositions of coexisting minerals (ol, opx, and cpx) from peridotite xenoliths entrained in the Hannuoba Tertiary basalts, North China Craton, provide insight into Li isotopic fractionation between mantle minerals during melt-rock interaction in the considerably thinned lithospheric mantle. Bulk analyses of mineral separates show significant enrichment of Li in cpx (2.4-3.6 ppm) relative to olivine (1.2-1.8 ppm), indicating that these peridotites have been affected by mantle metasomatism with mafic silicate melts. Bulk olivine separates (δ7Li ∼ +3.3‰ to +6.4‰) are isotopically heavier than coexisting pyroxenes (δ7Li ∼ -3.3‰ to -8.2‰ in cpx, and -4.0‰ to -6.7‰ in opx). Such large variation suggests Li elemental and isotopic disequilibrium. This conclusion is supported by results from in situ SIMS analyses of mineral grains where significant Li elemental and isotopic zonations exist. The olivine and opx have lower Li concentrations and heavier Li isotopes in the rims than in the cores. This reverse correlation of δ7Li with Li concentrations indicates diffusive fractionation of Li isotopes. However, the zoning patterns in coexisting cpx show isotopically heavier rims with higher Li abundances. This positive correlation between δ7Li and Li concentrations suggests a melt mixing trend. We attribute Li concentration and isotope zonation in minerals to the effects of two-stage diffusive fractionation coupled with melt-rock interaction. The earliest melts may have been derived from the subducted oceanic slab with low δ7Li values produced by isotopic fractionation during the dehydration of the seawater-altered slab. Melts at later stages were derived from the asthenosphere and interacted with the peridotites, producing the Li elemental and isotopic zoning in mineral grains. These data thus provide evidence for multiple-stage peridotite-melt interaction in the lithospheric mantle beneath the northern North China Craton.

Original languageEnglish
Pages (from-to)4327-4341
Number of pages15
JournalGeochimica et Cosmochimica Acta
Volume71
Issue number17
DOIs
Publication statusPublished - Sep 1 2007

ASJC Scopus subject areas

  • Geochemistry and Petrology

Fingerprint Dive into the research topics of 'Lithium isotopic systematics of peridotite xenoliths from Hannuoba, North China Craton: Implications for melt-rock interaction in the considerably thinned lithospheric mantle'. Together they form a unique fingerprint.

  • Cite this