Major element compositions of garnet, clino-pyroxene, orthopyroxene and spinel 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 in-creasing temperature and pressure from core to rim for granulites. In contrast, mantle xenoliths with core tempera-ture > 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 prod-ucts of the transition from granulite to eclogite metamor-phism corresponding to the increasing temperature and pressure. Together with previous studies, it is suggested that the P-T changes preserved in the xenoliths are related to lithospheric thickening and subsequent thinning prior to their eruption in the Cenozoic.
LIU YongshengGAO ShanLIU XiaomingCHEN XiaomingZHANG WenlanWANG Xuance
The Qianlishan granite, which is closely related to theShizhuyuan tungsten polymetallic mineralization, is aluminous alkali-type granite. The intimate temporal and spatial association among the basaltic, syenite and granitic rocks in the mining area, and their major and trace ele-ments, and Nd, Pb, Sr, O isotopic compositions indicate that the crustal-mantle interaction probably was an important constraint on, and participated in, the formation of the superlarge ore deposit.
Using the in situ zircon U-Pb dating method of LA-ICPMS, we analyzed the 31 Ma old SHRIMP U-Pb age of the Yongsheng nepheline syenite from southern Jilin Province under different spot sizes. The obtained ages are comparable with that of SHRIMP in both accuracy and precision. The age is also identical to that of the Yinmawanshan gabbro from the Liaodong Peninsula within error. Both the Yongsheng nepheline syenite and the Yinmawanshan gabbro represent the youngest known exposed intrusions in northeastern and even eastern China. The results indicate the Eocene mantle-derived magmatic underplating, and the rapid crustal uplifting of this region since 30 Ma. The analyses also document extremely high LREE concentrations and relatively flat REE patterns for the zircons from the Yongsheng nepheline syenite, which represent a new type of zircon REE pattern.
