Microanalysis of the Carbon Isotopic Composition in Diamonds from Shangdong of China by Secondary Ion Mass Spectrometry

Multi-stage growth and its significance in Shandong diamonds, China has been comprehensively studied, whereas microanalysis of δ¹³C is absent for diamonds at different stage and inner variation. 10 gem-quality Shandong diamond plates were investigated by Second Ion Mass Spectrometry (SIMS) and cathodoluminescence. It was found that the carbon isotopic composition of Shandong diamonds varies over a narrow range, from -5.6‰ to -2.01‰ with an average δ¹³C of -3.63‰. The range was generally in accordance with the previously studied carbon isotope compositions (δ¹³C values from -14.71‰ to -0.46‰, mainly lying between -9‰ and -4‰) of diamonds in the North China Croton, which was also within the range of δ¹³C values of global peridotitic diamonds and mantle(-8‰--2‰). Associated with cathodoluminescence imaged growth zones, variations of δ¹³C within a diamond from core to rim were concluded. δ¹³C trends to heavier from core to rim within the same growth zone, while the variations are different between multi-phase growth zones. The variations of δ¹³C values in diamonds reveal complication of growth environment and conditions in the region, also provide quantitative data to study the mantle carbon cycle in the North China Croton.