On the significance of temperatures derived from major element and REE based two-pyroxene thermometers for mantle xenoliths from the North China Craton

Abstract

Thermal evolution of the North China Craton (NCC) has been a subject of extensive geochemical and geophysical investigations. To better constrain the thermal state of lithospheric mantle beneath the NCC, we calculated and compared equilibrium or closure temperatures for peridotite and pyroxenite xenoliths from the NCC lithospheric mantle using major element-based two-pyroxene thermometers and a REE-based two-pyroxene thermometer. Samples included in this study are ancient refractory peridotites entrained by Early Cretaceous high-Mg diorites from Fushan within the central NCC, peridotites with varying chemical compositions and rhenium-depletion model ages entrained by younger than 100Ma alkali basalts from the central and eastern NCC, and pyroxenites entrained by Early Cretaceous alkali basalts from Feixian and Fangcheng within the eastern NCC. The Fushan peridotites have low major element-derived temperatures and slow cooling rates, owing to the shallow intrusion of their host diorites. The peridotites in younger than 100Ma alkali basalts have a more complicated thermal history. The Fexian and Fangcheng pyroxenites have relatively high temperatures and moderate to fast cooling rates. The present thermometric data, combined with the published petrologic, geochemical, and seismic observations, provide new insight into the thermal state and thermal evolution of the NCC lithospheric mantle in the Mesozoic and Cenozoic.