Adakitic rocks and destruction of the North China Craton: Evidence from experimental petrology and geochemistry

Abstract

The general temporal-spatial consistency for the formation of adakitic rocks and lithospheric thinning in northern China provide a window to examine the processes and mechanism for the destruction of the North China Craton. With experimental petrology data, this paper demonstrates that the adakitic rocks in northern China are the products of partial melting of middle- to high-potassic metabasalts at the base of the lower continent crust. Based on the TiO2 solubility model, many adakitic rocks in Dabie, Jiaodong and the northern part of the craton appear to have been saturated with TiO2. This indicates the presence of a Ti-rich accessory phase in their source regions. This phase must be rutile based on the decreasing Nb/La with increasing La/Yb in the adakitic rocks. The adakitic magmas were, thus, derived from a depth of more than 50 km, based on pressures (higher than 1.5 GPa) for the stability of rutile in a metabasalt system. Because present-day crustal thickness is generally only 35 km, we suggest that the destruction of the North China Craton may have led to at least 15 km of thinning or delamination of the crust.