Mineral Chemical Characteristics And Geological Significance Of Spinel From Mantle Xenoliths In Hebi Region Henan Province

Hebi lies in the transitional zone between the damaged area in the east and the relatively stable area in the west of the north China Craton.The deep-seated magmatic rocks such as Kimberlite and Olivine porphyrite in Hebi area,which carry a lot of mantle xenoliths,are a mantle window for studying the north China Craton.In this paper,the mineral chemistry of spinel in Mantle xenoliths carried by Tumen Kimberlite and Shangyu porphyrite in the Hebi area is reported,and the lithospheric mantle properties in the Hebi area are discussed.The main xenoliths in Kimberlite are lherzolite and the main minerals are Olivine+pyroxene+spinel.The xenoliths are ellipsoidal in shape and the size of xenoliths is 2?10 cm.Most of Olivine has been altered into Serpentine and TALC minerals due to strong weathering of Lherzolite,and the main mineral composition of Shangyu Olivine porphyrite is pyroxene and Olivine,the Matrix is aphanitic and pyroxene crystallite.The mantle xenoliths carried by porphyry are mainly spinel Harzburgite,spinel lherzolite and Garnet lherzolite.Spinel lherzolite are generally oval,breccia-shaped,the size of the General 2?6cm.The xenoliths are yellow-green in color and have a granular structure consisting mainly of forsterite,enstatite,chrome diopside and chrome spinel.The spinel Mg~# in mantle xenoliths carried by Kimberlite,Bumin Qaghan is between 21.58 and 78.66,Cr~#between 18.08 and 73.97,and the spinel Mg~#in mantle xenoliths carried by Shangyu are between 48.96 and 77.00,Cr~#between 18.78 and64.10.The comparison with the mantle spinel from Mengyin County,changle-shanwang and Hannuoba shows that the spinel mantle of Tumen and Shangyu is between the refractory mantle and the full mantle,and the transitional lithospheric mantle is dominant.The calculation of spinel-olivine mineral temperature-pressure gauge shows that the temperature of Tumen and Shangyu is mainly from 1031°C to1100°C,the pressure is from 1.70 Gpa to 1.90 Gpa,and the mantle thermal current is obviously on the high side,may Be related to the destruction of the north China Craton.According to the empirical formula,the partial melting degree experienced by the Lherzolite xenoliths in Tumen Kimberlite is between 6.88%and 18.83%,and the mean is 14.68%,and the partial melting degree of the Lherzolite xenoliths in Tumen Kimberlite is between 6.88%and 18.83%,respectively The partial melting degree of the Shangyu Olivine porphyrite is between 2.15%and 18.89%,and the average is14.01%.The partial melting of the lithospheric mantle of Tumen and Shangyu is equivalent.Compared with Hannuoba and Changle-Shanwang,it is concluded that the lithospheric mantle in Hebi area is not typical cratonic mantle and should be transitional lithospheric mantle.