Destruction of Archean lower crust recorded in granulite and pyroxenite xenoliths of Mesozoic basalts from Western Liaoning, North China Craton

Lower crustal processes played a key role during the destruction of the North China Craton. Petrological and geochemical analyses were performed on the granulite and pyroxenite xenoliths in the late Cretaceous basalt from Western Liaoning of the North China Craton to investigate the nature and evolution of the lower crust during the Mesozoic. The granulite xenoliths are predominantly intermediate–silicic granulite with subordinate basic granulite. The intermediate–silicic granulites exhibit relatively low Mg# values (0.46–0.63), positive Eu, Pb and Sr anomalies, a large range of Sr–Nd–Pb isotopic compositions and negative correlations between 87Sr/86Sr and 143Nd/144Nd ratios. The sample HS20-19 shows the lowest SiO2 and MgO contents than that of other intermediate–silicic granulites. Generally, the intermediate–silicic granulites have mineralogical and whole-rock geochemical affinities to the Archean granulite terrains of the North China Craton. In contrast, the basic granulite has a higher Mg# value (0.73), and depletions of La and Sr, but similar Sr–Nd–Pb isotopic compositions to the intermediate–silicic granulite xenoliths and terrains. These observations indicate that most intermediate–silicic granulites represent modified Archean lower crust by underplated magma, whereas HS20-19 and the basic granulite can be explained as restites left after partial melting of the ancient lower crust. The pyroxenite xenoliths exhibit a cumulate texture, variable Mg# values (85.9–88.6), and convex-upward rare-earth element patterns with high-field-strength elements depletions in the clinopyroxene. 87Sr/86Sr ratios (0.7036–0.7063) are negatively correlated with Mg# values and positively correlated with Ba and Pb contents in the clinopyroxene. These observations imply that the pyroxenite xenoliths originated as cumulates from an asthenospheric magma and were contaminated by the lower crust at the crust–mantle transition. All xenoliths experienced decompression event induced by the lithosphere extension in the early Cretaceous. Combined with the previous studies on the Mesozoic volcanic rocks from the Western Liaoning, we conclude that the continuous magmatic underplating not only formed the pyroxenite cumulates but also provided heat for remelting of the ancient lower crust, resulting in the formation of voluminous intermediate–silicic volcanic rocks during the Mesozoic. These processes led to the transformations of the Archean lower crust beneath the Western Liaoning and the entire North China Craton.