河南鹤壁地区金伯利岩中地幔包体矿物化学特征  

Mineral Chemical Study on Mantle Xenoliths from Kimberlites in Hebi Region, North China Craton

作　　者：侯广顺[1,2,3] 向世红 齐永安[1] 支风岐 王明国 周雪 林刘军 李明[1] 吴成斌[1] 

机构地区：[1]河南理工大学资源环境学院,河南焦作454003 [2]河南省有色金属地质勘查总院,河南郑州450052 [3]中国地质大学地质过程与矿产资源国家重点实验室,湖北武汉430074

出　　处：《矿物学报》2016年第3期318-328,共11页Acta Mineralogica Sinica

基　　金：国家自然科学基金项目(批准号:41003015);河南理工大学与河南省有色金属地质勘查总院联合培养博士后项目;地质过程与矿产资源国家重点实验室开放课题项目(编号:GPMR201011);河南省博士后基金项目;河南理工大学博士基金项目

摘　　要：河南鹤壁地区位于太行山构造带上,该区金伯利岩中的地幔包体携带有岩石圈地幔的丰富信息。本文报道了石榴石二辉橄榄岩包体中的镁橄榄石和镁铝榴石的矿物化学特征。金伯利岩中地幔包体的镁橄榄石I(Mg~#)为91.7±0.2(n=69)。与鹤壁地区尖晶石相方辉橄榄岩相比,I(Mg~#)略偏小,指示二辉橄榄岩经历的熔融程度较低,具有过渡型地幔的特征。根据Cr_2O_3含量,镁铝榴石可以划分为高铬系列和低铬系列两类。橄榄石-石榴石矿物温压计计算表明,包体压力在1.7~2.5 GPa之间(55~80 km),温度在641~1055℃之间,对应的大地热流值为50~60m W/m^2,甚至更高。指示金伯利岩侵位时对应于较高的大地热流条件。根据Grutter的镁铝榴石划分方案,镁铝榴石主要划分为G9型、G3和G4型,其中G3和G4型镁铝榴石记录了岩石圈地幔被交代的过程。根据温压条件及岩石圈地幔性质,可以认为鹤壁地区不具有形成金刚石矿的深部地质条件。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 Cr2O_3 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 m W/m^2. 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.

关 键 词：金伯利岩 地幔包体 石榴石二辉橄榄岩 镁橄榄石 镁铝榴石 

分 类 号：P579[天文地球—矿物学] P581[天文地球—地质学]