Study On The Diamond And The Inclusions From North Craton Area

Shandong Mengyin and Liaoning Fuxian are the two main areas producing diamond-bearing kimberlite of North China Craton.Based on the study of diamond and mineral inclusions,the characteristics of the lithospheric mantle of North China Craton are discussed,which provides more evidence for revealing the thinning mechanism of North China Craton lithosphere.Thus diamond samples from Liaoning Fuxian and Shandong Mengyin as the research object were selected for this study.Current research direction of diamond and its inclusions were reviewed,and the diamonds were tested through microscope,SIMS,CL,FTIR,SEM,EDS,EPMA,Raman,etc,to give more information of the diamonds themselves and their inclusions,and thus the following aspects were obtained:The morphology of most diamonds was mainly single crystal,of which the crystal form is octahedron and rhombic dodecahedron.The growth patterns of the diamonds were mainly concentric octahedral bands,following with a few patches of heterozygous or no obvious growth band structure.Different surface microscopic characteristics were related with different crystals.Triangular thin layer,shields lamine inverted triangular erosion like;diamond dodecahedral surface of multiple pieces of hill-like bulge,hexagonal melting pits.Whether it is crystal in the diamond-shaped dodecahedron,crystal surface of the various patterns and the cathode light of the instructions of the erosion structure,are representative of the formation of the diamond suffered a different degree of erosion.The inclusions of diamonds in this study were mainly visible graphite,olivine,pyroxene,magnesium aluminum garnet and sulfides,mostly P type,together with one diamonds containing inclusions of low Ni and iron based metallic phase indicating E type,which gave new basis of the existence of eclogites below North China Craton region.The?¹³C value of some diamond samples in Mengyin ranged from--11.02‰to-3.96‰,of which the average ranged from-9.07‰to 1.33‰,falling in the range of North China Cratonindicating carbon source from lithospheric mantle.At the same time,the micro-FTIR test of sample Y-7 and Y-28 in Mengyin area of Shandong Province was carried out.It was found that the nitrogen content varied from core to edg between 849.16?663.52ug/g and 1089.57?731.92ug/g,consistent with the range of 600-1500ug/g of the upper mantle diamond by quantitative calculation,and the age was 0.71?0.77Ga,1.28?1.39Ga respectively.Previous application of this method showd that the age range of the diamond in the mantle was between 0.202 and 1.07Ga.The Y-7 and Y-28 are formed in different periods and are located all before the kimberlite magma arriving,providing evidence of multi-source of diamond in the Noth China Craton.Y-7 from Shandong Mengyin region were selected for special attention for the iron based metallic phase inclusione.The total nitrogen content N_T of diamontogether with the concentric band structure indicated formation of mantle depth range,and low(<3 wt.%)content suggested a eclogitic formation.The mineral assemblage of the inclusions indicates reducing environment with oxygen fugacity close to the IW buffer,which provides new evidence that the natural diamond can be formed in the low oxygen fugacity condition,and also revealed the mantle of the North China Craton has local areas with oxygen fugacity below the IW area...