Pyroxenite-derived early cretaceous lavas in the liaodong peninsula: Implication for metasomatism and thinning of the lithospheric mantle beneath North china craton
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The Xiaoling lavas, erupted at ca. 110 Ma in the Liaodong Peninsula, North China, provide vital constraints on the thermochemical state of subcontinental lithospheric mantle (SCLM) during the destruction of the craton. The Xiaoling lavas comprise basalt, andesite and dacite. They are characterized by depletion of high field strength elements (HFSE), enrichment of large ion lithophile elements (LILE) and EM1-like Sr–Nd isotopic compositions (εNd(t) = − 8.7–−16.0; 87Sr/86Sri = 0.7046–0.7054), consistent with a derivation from the SCLM. With the exception of TiO2, the studied samples have major element compositions similar to those of experimentally determined partial melts of volatile-free Mid-Ocean-Ridge Basalt (MORB)-like eclogite at 3–5 GPa, but differ from anhydrous peridotite-derived melts. The olivine phenocrysts of the basaltic samples have high Ni and Fe/Mn, and low Ca contents, which are typical of the olivines crystallized from melts derived from a garnet pyroxenitic mantle source. This suggests that the Xiaoling lavas were derived from a pyroxenitic mantle source, which may have been formed by the solid-state reaction between recycled crustal materials and their surrounding peridotites. The presence of abundant amphibole phenocrysts in the Xiaoling lavas suggests a highly hydrated SCLM in this region. The high Rb/Sr but low initial 87Sr/86Sr ratios of the Xiaoling samples require a recent metasomatism in the mantle source, which is most likely related to the Pacific subduction. The genesis of the Xiaoling lavas therefore highlights the important role of water and Pacific subduction in the destruction of the North China Craton.
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