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North China lithospheric thinning and accretion processes: Constraints on Cenozoic volcanic and mantle-derived xenoliths TEXT SIZE: A A A

Typical columnar profiles of (Late Mesozoic to) Cenozoic volcanics and mantle-derived xenoliths in part of the basalts in North China and Northeast China were selected as the subject of the study. By means of chronological, petrological and geochemical tracking techniques, the rules governing the temporal and spatial evolution of volcanoes were defined, and emphasis was put on the rules of volcanism occurring in several key periods, such as the period for transition from magma-enriched mantle source to depleted mantle source, the period from the end of Cretaceous to early Cenozoic, and the period ever since Oligocene. The depth of volcanic origin, the relative contribution to magmatic chamber by lithosphere/asthenosphere, features and water content of primitive magma, conditions for mantle melting, and the trend of temporal evolution of these indices were studied. The results can help to reveal the internal connections between magmatic origin and lithospheric evolution as well as structural control, and to establish a complete lithospheric evolution sequence of the study area. Based on the Os-Hf isotope composition of mantle-derived xenoliths and the geothermal gradient of the lithosphere, the composition-age structure of the lithosphere can be constructed to validate the mechanism for lithospheric thinning; When the composition and evolution of basalts and mantle-derived xenoliths in east North China, west North China and Northeast China were compared with one another, the temporal-spatial inhomogeneity and the structural control elements for lithospheric thinning process can be revealed.

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