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Using basalt geochemistry to constrain Mesozoic-Cenozoic evolution of the lithosphere beneath North China Craton

XU Yi-GangKey Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China  
Because the composition of basalts depends on a number of factors including source characteristics, degree of partial melting, mantle temperature and lithospheric thickness, it can be used to constrain the mantle evolution.This paper describes how to use basalt geochemistry to constrain the lithospheric thickness and summarizes two major features regarding the evolution of Mesozoic-Cenozoic magmas in the North China craton:(a) there is a transition from enriched mantle-derived magmas to depleted mantle-derived basalts during the late Mesozoic, and these two stages are separated by a magmatic hiatus (~10 Ma); (b) the temporal variations in alkali content for Cenozoic basalts from western and eastern North China are different.All of these features can be understood in terms of a gradual increase in thermal gradient of the lithosphere during lithospheric thinning, the consumption of fusible components in the lithospheric mantle that cannot be re-supplied over a short period of time, and the lithospheric lid effect.The present interpretation yields important constraints on the time scale and mechanism of lithospheric thinning in North China.It also implies a temporally and spatially heterogeneous process for the destruction of the lithospheric keel beneath the North China craton.
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