Petrology and geochemistry of peridotite xenoliths from the Lianshan region: Nature and evolution of lithospheric mantle beneath the lower Yangtze block

Jianggu Lu, Jianping Zheng*, William L. Griffin, Chunmei Yu

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

35 Citations (Scopus)

Abstract

Lithospheric thinning beneath the North China Craton is widely recognized, but whether the Yangtze block has undergone the same process is a controversial issue. Based on a detailed petrographic study, a suite of xenoliths from the Lianshan Cenozoic basalts have been analyzed for the compositions of minerals and whole rocks, and their Sr-Nd isotopes to probe the nature and evolution of the subcontinental lithospheric mantle beneath the lower Yangtze block. The Lianshan xenoliths can be subdivided into two Types: the main Type 1 xenoliths (9-15% clinopyroxene and olivine-Mg#<90) and minor Type 2 peridotites (1.8-6.2% clinopyroxene and olivine-Mg#>90). Type 1 peridotites are characterized by low MgO, high levels of basaltic components (i.e., Al 2O 3, CaO and TiO 2), LREE-depleted patterns in clinopyroxenes and whole rocks, and relatively high 143Nd/ 144Nd (0.513219-0.513331) and low 86Sr/ 87Sr (0.702279-0.702789). These features suggest that Type 1 peridotites represent fragments of the newly accreted fertile lithospheric mantle that have undergone ~1% of fractional partial melting and later weak silicate-melt metasomatism, similar to Phanerozoic lithospheric mantle beneath the eastern North China Craton. Type 2 peridotites may be shallow relics of the older lithospheric mantle depleted in basaltic components, with LREE-enriched and HREE-depleted patterns, relatively low 143Nd/ 144Nd (0.512499-0.512956) and high 86Sr/ 87Sr (0.703275-0.703997), which can be produced by 9-14% partial melting and subsequent carbonatite-melt metasomatism. Neither type shows a correlation between equilibration temperatures and Mg# in olivine, indicating that the lithospheric mantle is not compositionally stratified, but both types coexist at similar depths. This coexistence suggests that the residual refractory lithospheric mantle (i.e., Type 2 peridotites) may be irregularly eroded by upwelling asthenosphere materials along weak zones and eventually replaced to create a new and fertile lithosphere mantle (i.e., Type 1 xenoliths) as the asthenosphere cooled. Therefore, the subcontinental lithospheric mantle beneath the lower Yangtze block shared a common evolutional dynamic environment with that beneath the eastern North China Craton during late Mesozoic-Cenozoic time.

Original languageEnglish
Pages (from-to)161-175
Number of pages15
JournalGondwana Research
Volume23
Issue number1
DOIs
Publication statusPublished - Jan 2013

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