河南省鹤壁地区地幔捕掳体中尖晶石的矿物化学特征及其地质意义

Mineral chemical characteristics and geological significance of spinel from mantle xenoliths in Hebi region,Henan province

河南省鹤壁地区位于华北克拉通东部破坏区与西部相对稳定区的过渡带上,出露有大量的地幔捕掳体,是研究华北克拉通的一个地幔窗口。本文分析了鹤壁地区土门金伯利岩和新生代上峪橄辉玢岩所携带的地幔捕掳体中尖晶石的矿物化学特征,并探讨该地区的岩石圈地幔性质。土门金伯利岩所携带的地幔捕掳体中的尖晶石Mg^#介于21.58~78.66,Cr^#介于18.08~73.97;上峪橄辉玢岩所携带的地幔捕掳体中尖晶石Mg^#介于48.96~77.00,Cr^#介于18.78~64.10。山东蒙阴地区的地幔包体代表华北古生代古老难熔型地幔,昌乐-山旺和河北汉诺坝等新生代地幔代表华北中新生代新生饱满型地幔。与山东蒙阴、昌乐-山旺、河北汉诺坝等地区地幔尖晶石的对比表明,土门和上峪的尖晶石相地幔介于难熔型地幔和饱满型地幔之间,以过渡型岩石圈地幔为主。尖晶石-橄榄石矿物温度压力计算表明,土门和上峪的捕掳体温度主要集中在1031~1090℃,压力集中在1.70~1.88 GPa,处于明显偏高的地幔热流状态,可能与华北克拉通的破坏有关。

Hebi region,Henan province is located in the transition belt between the destroyed part of the eastern and the relative stable part of the western of North China Craton(NCC).There are a large number of mantle xenoliths exposed,which is a mantle window for the study of the NCC.The mineral chemical characteristics of spinels in mantle xenoliths carried by Tumen kimberlite and Cenozoic Shangyu olivine-pyroxene porphytite in Hebi region were analyzed and the character of lithosphere mantle in this area was discussed.The Mg^#and Cr^#of spinels in mantle xenoliths from Tumen kimberlite were between 21.58~78.66 and 18.08~73.97 respectively.The Mg^#and Cr^#of spinels in mantle xenoliths from Cenozoic Shangyu olivine-pyroxene porphytite were 48.96~77.00 and 18.78~64.10 respectively.Mantle xenoliths in Mengyin area of Shandong province represented the paleozoic refractory mantle of NCC,while the mantle xenoliths in Changle-Shanwang and Hannuoba in Hebei province represented the Meso Cenozoic and Cenozoic plump mantle.By comparison with spinels in mantle xenoliths from Mengyin region,Changle-Shanwang region,Shandong province and Hannuoba region,Hebei,the spinel phase mantle of Tumen and Shangyu was between the refractory mantle and the plump mantle,and the transitional lithospheric mantle was the main one.The calculation of spinel olivine mineral temperature manometer showed that the temperature of the xenoliths in Tumen and Shangyu were mainly concentrated in 1031~1090℃,and the pressure was concentrated in 1.70~1.88 GPa,which was in a obviously high mantle heat flow state,and that might be related to the destruction of NCC.