ABSTRACT
The spinel/garnet lherzolite in Cenozoic basalt of eastern China and the Al-poor pyroxene bearing garnet lherzolite in ultrahigh-pressure metamorphism zone of Dabieshan-Subei-Jiaodongnan of Center-East China directly provide us with the natural samples of phase transition from spinel to garnet and from pyroxene to garnet occurring under continental upper mantle condition. We have carried out high temperature and high pressure experimental research on the above mentioned phase transitions using natural mineral and rock specimens obtained from mantle xenolith in Cenozoic basalt as the initial materials for the experiment. The experimental results provide the information about the petrographic characteristics and the change of mineral chemical composition of phase transition under different P-T conditions. We believe that there exists a phase transition zone of spinel lherzolite to garnet lherzolite with thickness of few km to about ten km at the depth of 55–70km, and we infer that the upper mantle garnet peridotite is transformed with the increase of depth from Al-rich pyroxene garnet peridotite (70–120km) to Al-poor pyroxene garnet peridotite(more than 120–150km) in continental upper mantle of eastern China
