Temporal and spatial distribution of Mesozoic mafic magmatism in the North China Craton and implications for secular lithospheric evolution

Abstract

AbstractMesozoic mafic magmatism in the North China Craton shows a clear temporal and spatial distribution. Mesozoic mafic volcanism occurred dominantly in the northern and southern margins of the craton, with episodic eruptions from Early Jurassic to Late Cretaceous time. In contrast, Mesozoic mafic magmatism, which produced gabbroic to dioritic intrusive complexes, occurred in the centre of the craton in areas such as the Taihang Mountains and the Luzhong region, and all the complexes were intruded at almost the same time in the Early Cretaceous. This temporal and spatial distribution of Mesozoic mafic magmatism shows a strong heterogeneity of the Late Mesozoic lithospheric mantle beneath the North China Craton and a secular evolution of the lithospheric mantle beneath it. The lithospheric mantle beneath the Luzhong region is slightly isotopically enriched; that beneath the Taihang Mountains has an EM1 character in Sr and Nd isotopic features (87Sr/86Sr)i=0.7050–0.7066; εNd(t)=−17 to −10); and it possesses EM2-like characteristics (87Sr/86Sr)i up to 0.7114) beneath the Luxi–Jiaodong region. The general enrichment suggests that the Mesozoic lithospheric mantle was distinctive compared with Palaeozoic and Cenozoic counterparts. The secular evolution of this variably enriched Mesozoic lithospheric mantle requires a considerable modification, transformation and reconstruction of the lithospheric mantle beneath the craton in Late Mesozoic time. The elemental and isotopic compositions and the coherence of the lithospheric changes with the formation of circum-craton orogenic mobile belts indicate that these rapid lithospheric changes and corresponding lithospheric thinning were tectonically related to the multiple subduction and subsequent collisions of circum-craton blocks. Dehydration melting of subducted oceanic and continental crustal materials produced silicic melts that migrated up and reacted with lithospheric peridotites to generate more fertile lithospheric mantle (‘wet’ low-Mg peridotites plus pyroxenite veins). This is demonstrated by the fact that beneath the southern and northern margins the mantle was strongly modified, but beneath the central craton the effects were less marked. Compositional mapping of olivine from mantle peridotitic xenoliths and xenocrysts entrained in Mesozoic and Cenozoic basalts and mafic rocks throughout the craton suggests a similar framework. The North China Craton provides convincing evidence that the nature of the refractory lithospheric mantle was considerably changed in chemical composition through time, and that the lithospheric destruction was triggered by multiple circum-craton subductions and collisions.