Abstract:

Abundant pyroxenite xenoliths were found from the Cenozoic Changle basalts, an area distributing near the Tanlu fault zone.  These xenoliths can be subdivided into three types according to the petrochemistry including major and trace elements.  Samples type I and type II, with geochemistry respectively corresponding to the series Cr and Al pyroxenite xenoliths from Hannuoba and Yangyuan Cenozoic basalts(Hebei Province), are interpreted as products derived from the high pressure crystal-segregation at mantle-crust transition zone or upper part of the subcontinental lithospheric mantle(SCLM). Trace element compositions of the type II xenoliths suggest the involvement of crust components in these samples.  Type III pyroxenites are compositionally similar to those containing garnet from Hannuoba basalts, but different from each other with trace elemental characteristics of the Ocean Island Basalt(OIB)or Normal Mid-Ocean Ridge Basalt(N-MORB).  Comparing to the simpler Cenozoic SCLM, more complex components from these pyroxenite xenoliths within the mantle-crust transitional zone beneath the area imply the replacement of the cratonic mantle by the newly accreted lithosphere from deep to shallow due to the upwelling asthenosphere.

Key words: pyroxenite xenolith, petrochemistry, lithospheric evolution, Changle basalt, North China Craton