Temperature and pressure condition of garnet lherzolite and websterite from west Qinling, China

Abstract

The mineral thermobarometry proposed in literature is used to calculate the equilibrium temperature and pressure of garnet lherzolite and websterite xenoliths within the Cenozoic kamafugite from west Qinling, Gansu Province, China. The results show that the equilibrium temperature and pressure of garnet lherzolites and websterite and 1127–1266°C, 2.9–3.6 Gpa and 1169–1248°C, 2.8–3.2 Gpa respectively. The equilibrium peressures reach or exceed the equilibrium peressure of spinel lherzolites (2.0–3.0 GPa), and fall into the stability range of garnet peridotite. The equilibrium temperature of the xenoliths reach or exceed the ocean geotherm, identical with the melting temperature of kamafugite magma determined by experiments under the conditions of post-orogenic lithosphere extension. So the thermal state of Cenozoic mantle of the west Qinling may be fit to generate the kamafugite magmatism. The research on petrology-mineralogy and geobarothermometry of the xenoliths shows that both garnet lherzolite and websterite are mantle components of the west Qinling, and may be considered as source rocks of the Cenozoic kamafugite magma.