HOU Guang-shun1,2,3, XIANG Shi-hong2, QI Yong-an1, ZHI Feng-qi2, WANG Ming-guo2, ZHOU Xue2, LIN Liu-jun1, LI Ming1, WU Cheng-bin1
(1. Institute of Resources & Environment, Henan Polytechnic University, Jiaozuo 454003, China;
2. General Institute of Non-ferrous Metals Geological Exploration, Zhengzhou 450052, China;
3. China State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China)
Abstract: Hebi region is located on Taihangshan tectonic belt, and mantle xenoliths from kimberlites of this region contain much information about the lithosphere mantle of North China Cration (NCC). Chemical characteristics of olivines and pyropes in mantle xenoliths, garnet lherzolites, brought out by the kimberlites were firstly reported in this paper. The mean I(Mg#) of the forsterites from lherzolites is 91.7±0.2 (1σ, n=69). By comparison with shallow relict spinel harzburgites, the I(Mg#) of olivines from lherzolites is low, suggesting that the lherzolites experienced a lower degree of partial melting than the spinel harzburgites did, and that the lherzolites derived from a transitional mantle. Based on their Cr2O3 content, pyropes can be subdivided into high- and low-Cr series. From olivine-garnet geothermobarometer, the estimated p and t for the xenoliths are 1.7－2.5 GPa (55－80 km in depth) and 641－1055 ℃, respectively. The mantle heat flow in this region may be as high as 50－60 mW/m2. This indicates that the kimberlites formed at high heat flow, and an active tectonic setting. According to the classification scheme of Grutter for garnet from kimberlite, pyropes can mainly be subdivided into G9-, G3- and G4-type. The occurrence of G3- and G4-type pyropes suggests that the Hebi mantle xenoliths have been metasomatized, and indicates the lithosphere destruction of NCC. From the P-T condition and lithosphere mantle character, it can be concluded that there is no geological conditions to form diamond mine in Hebi region.
Email: houguangshun@163.com
Keywords: kimberlite; mantle xenolith; garnet lherzolite; forsterite; pyrope
ACTA MINERALOGICA SINICA Vol. 36, No. 3, 2016, Page 318-328
