Transformation of lithospheric mantle through peridotite-melt reaction: A case of Sino-Korean craton

Early Cretaceous Fangcheng basalts, erupted in Luxi region of Shandong Province, China, contain olivine xenocrysts with clear compositional zonations, which provide evidence for important mantle-melt reactions. These zoned olivines are fine-grained (200∼900 μm) and the core of the relatively larger grains have compositions (such as Mg# = 88∼92) similar to those of olivines from the mantle peridotitic xenoliths entrained in Cenozoic basalts from the Sino-Korean craton and their rims (Mg# = 76∼83) are compositionally close to those of the olivine phenocrysts from the host basalts. These compositional features as well as textural characteristics such as rounded and embayed crystal shape, well-developed cracks and grain sizes demonstrate that these olivines are mantle xenocrysts disaggregated from the lithospheric peridotites. The zoned texture was formed through rapid reaction between olivine and host melt. This may suggest that mantle-melt reaction was once very significant in the Mesozoic lithospheric mantle beneath the southeastern portion of the Sino-Korean craton, which we consider to be responsible for the replacement of lithospheric mantle from the Paleozoic refractory (high-Mg) peridotitic mantle to the late Mesozoic fertile (low-Mg) and enriched mantle with the loss of more than 120 km Archaean lithospheric keel in the region.