Thermodynamic evolution of lithosphere of the North China craton： Records from lower crust and upper mantle xenoliths from Hannuoba

Lithospheric thinning in East China attracts much attention of geologists. In many cases where a lithospheric thinning is inferred, the trigger for instability is a preced-ing episode of crustal thickening by the continental colli-sion1]. Lithospheric processes (e.g. lithospheric thinning) could be recorded by the thermal history of the lower crustal and upper mantle xenoliths. Xu et al.2] suggested that the cooling (from >1200 to 850℃) recorded by spinel harzburgite from Northeast China …

Thermodynamic evolution of lithosphere of the North China craton: Records from lower crust and upper mantle xenoliths from Hannuoba

Major element compositions of garnet, clinopyroxene, orthopyroxene andspinel in the garnet-bearing lower crust and upper mantle xenoliths from Hannuoba, North China craton are analyzed by the electron microprobe (EMP). The pressure-temperature estimates reveal the increasing temperature and pressure from core to rim for granulites. In contrast, mantle xenoliths with core temperature > 930℃ recorded a history of decrease in temperature and pressure. However, those with core temperature < 930℃ show a negligible change. The final pressures recorded by these xenoliths cluster at 0.9-1.5 GPa. The presence of high- Na2O cpx in granulite xenoliths suggests that they are products of the transition from granulite to eclogite metamorphism corresponding to the increasing temperature andpressure. Together with previous studies, it is suggested that the P-T changes preserved in the xenoliths are related to lithospheric thickening and subsequentthinning prior to their eruption in the Cenozoic.