Nature and evolution of the Cenozoic lithospheric mantle beneath the northeastern Yangtze Craton, China: Insights from Sr-Nd-Pb-Os isotopes of peridotite xenoliths

Abstract

The eastern North China Craton has undergone significant modification and destruction, with over 100 km of ancient lithospheric mantle lost from the Paleozoic to the Cenozoic. However, it remains unclear if the neighboring eastern Yangtze Craton, which is part of eastern China, underwent similar deep geological processes within the same geodynamic setting. This study examines peridotite xenoliths hosted by the Cenozoic basalts from the Subei Basin, located in the northeastern Yangtze Craton, using integrated analyses of petrology, major-trace elements, and Sr-Nd-Pb-Os isotopic compositions. The spinel lherzolite xenoliths exhibit porphyroclastic and granular textures, reflecting fertile and juvenile mantle compositions (whole-rock Al₂O₃ = 2.09–3.73 wt%, Fo = 89.1–90.2). The Os isotopic ratios (¹⁸⁷Os/¹⁸⁸Os = 0.1208–0.1256) are consistent with those of the asthenosphere, as observed in abyssal peridotites. Two distinct trace element patterns are identified in the clinopyroxenes. Type-1 clinopyroxenes are slightly enriched in LREE and exhibit depleted Sr-Nd-Pb isotopic compositions (⁸⁷Sr/⁸⁶Sr = 0.7026–0.7031, ɛ_Nd = 8.9–12.3, (²⁰⁶Pb/²⁰⁴Pb)_i = 17.840–18.135, (²⁰⁷Pb/²⁰⁴Pb)_i = 15.419–15.474, (²⁰⁸Pb/²⁰⁴Pb)_i = 37.732–38.115). In contrast, Type-2 clinopyroxenes are slightly depleted in LREE and exhibit more depleted Sr-Nd-Pb isotopic ratios (⁸⁷Sr/⁸⁶Sr = 0.7022–0.7027, ɛ_Nd = 10.5–23.0, (²⁰⁶Pb/²⁰⁴Pb)_i = 17.114–17.856, (²⁰⁷Pb/²⁰⁴Pb)_i = 15.365–15.461, (²⁰⁸Pb/²⁰⁴Pb)_i = 37.011–37.728), resembling the depleted MORB mantle (DMM). These signatures and variations in trace elements and isotopes suggest that the peridotite xenoliths from the Subei Basin represent a newly accreted lithospheric mantle formed through the upwelling and cooling of the asthenosphere. Both peridotite types show low degrees of partial melting (<10 %), with Type-1 likely experiencing slight metasomatism from silicate melt derived from subducting sediments. Despite distinct characteristics, both types indicate similar equilibrium temperatures, suggesting a common depth of origin. The integrated petrological and geochemical characteristics of the peridotite xenoliths indicate that the Cenozoic subcontinental lithospheric mantle beneath the northeastern Yangtze Craton was newly accreted through rapid upwelling and cooling of the asthenosphere following delamination of the low part of lithosphere. This study investigates the transformation of the lithospheric mantle beneath the northeastern Yangtze Craton in response to the extensional setting induced by the subduction and rollback of the paleo-Pacific Plate, including the complete delamination of the ancient, refractory lithosphere, asthenospheric upwelling and cooling, and the formation of the juvenile, fertile lithospheric mantle.