Thermo-tectonic destruction of the archaean lithospheric keel beneath the sino-korean craton in china: evidence, timing and mechanism

Abstract

Sino-Korean Craton (SKC) in eastern China is an important natural laboratory for studying temporal change to the lithosphere because there is the jutaxposition of Ordovician diamondiferous kimberlites, Mesozoic lamprophyre-basalt and Cenozoic tholeiite-alkali basalts in this craton. While diamond inclusions, xenoliths and mineral concentrates in kimberlites indicate a thick (180 km), cold and refractory lithospheric keel beneath the SKC prior to the Palaeozoic, basalt-borne xenoliths reveal the presence of thin (<80 km), hot and fertile lithosphere in the Cenozoic. This indicates the dramatic change in lithospheric architecture during the Phanerozoic. Geochemical characterization of late Jurassic to recent basalts further suggests that the lithospheric destruction started since the Jurassic, probably due to the loss of physical integrity of the craton as a result of the Triassic collision between North China and Yangtze blocks. The replacement of old lithospheric keel by “oceanic” mantle has been accomplished during the late Cretaceous. Coupled thermo-mechanical and chemical erosion within the lithosphere-asthenosphere interface is considered as an important mechanism to thin the lithosphere. The lithospheric thinning may proceed with gradual upward migration of the lithosphere-asthenosphere boundary. Alternatively, the lithospheric thinning could proceed in the way that the old lithospheric mantle was penetrated and then desegregated by hot mantle materials which rise along vertical lithospheric shear zones and spread like mushroom clouds.