The Difference And Significance Of Growth Process Of The Diamond From Huabei Craton And Yangzi Craton

Microscopic characteristics,cathodoluminescence(CL) images and micro-infrared spectroscopy (FTIR) analysis of the diamonds from Huabei craton and Yangzi craton indicate that there are many differences between the two cratons in the external characteristics,the internal growth structure,the content and forms of the main impurity elements of diamonds.These differences reflect the different of growth process,condition and environment of diamonds from the two cratons.It is found that some differences exist in diamonds from two cratons by microscopic observation, such as shape,color,corrosion extend and so on.The main crystal form of the diamonds from Huabei craton is octahedral,and combination form is rare.However,there are more dodecahedral and combination form in diamonds of Yangzi craton.Most of Huabei craton diamonds are colorless or brown with adamantine luster,as well as colorless diamonds are rare in Yangzi craton, most are yellow series and bluish green series with oily-adamantine luster.The crystal perfection of diamonds from Huabei craton is worse than that of Yangzi craton,and the diamond deformation of Huabei craton is more serious.In addition,all of them have corrosion in varying degrees.The CL test shows that the main color of the CL images of diamonds from the two cratons is similar,usually is blue or green.The majority diamonds have homogeneous growth structure and simple octahedral growth zone structure,which show that most diamonds had a continuous growth process without significant corrosion.Diamonds of the two cratons have experienced a relatively homogeneous growth process,and the differences displayed mainly in the late growth stage.The CL styles of Huabei craton diamonds are usually regular with many zones,manifesting obviously as the layer-by-layer growth mode.Some diamonds manifested as linear layer-by-layer growth mode,some manifested as arc shaped or jagged layer-by-layer growth mode.However,Yangzi craton diamonds usually lack of zones,but some special CL styles appear in CL images,such as zonal-sectorial structure,sectorial structure,nonluminous blocky structure and so on. There are differences between Mengyin diamonds,Shangdong province and Wafangdian diamonds,Liaoning province in both the form and the complexity of the diamond CL zones. Mainly the growth process of Shandong diamond was more continuous than that of Liaoning diamond.The corrosion of Liaoning diamond was more serious than that of Shandong province in growth process.Besides,the corrosion of Liaoning diamond was happened generally in the medium-term growth process,but Hunan diamond generally suffered corrosion in the latter growth process.Moreover,it is found that there are two quite different CL patterns in the diamonds of Hunan,which represent two different patterns of growth.Whether it implies that Hunan diamonds were not from the same original rock depends on the further study.The micro-FTIR analysis reveals that there are type change of nitrogen and the strength change of hydrogen absorption peak in diamond from the core to the edge,which reflects the stage and heterogeneity of growth process.Quantitative analysis revealed that the N,H impurity content and mutative trend of diamonds from Huabei craton and Yangzi craton are also differences.The relative trends of H content trends of diamonds from the two cratons are totally opposite. The hydrogen relative content of Huabei craton diamonds from the core to the edge presents an overall downward trend,which shows the gradual consumption of hydrogen in diamond growth process.Nevertheless the hydrogen relative content of Yangzi craton diamonds from the core to the edge presents an overall upward trend,which shows the continuous replenishment of hydrogen in diamond growth process.The H content range of Liaoning diamond and Hunan diamond is distinctly greater than that of Shandong diamond.The change characteristics of H show that the deep mantle fluid environment of diamonds from the two mining area is different from a certain viewpoint,and it also indicates that the growth environment of Shandong diamond is more stable than Liaoning and Hunan diamond.The number of total nitrogen of the two cratons diamonds is discrepant.Yangzi diamonds have the highest N content and the widest range.The N content and range of diamonds from the two mining area of Huabei craton is more or less the same.A part of Shandong diamonds have high N_B%,which illustrates that this kind of diamond may have experienced a relatively higher retention temperature or a relatively longer retention time.The coated diamonds of Mengyin show different growth process from ordinary diamonds.The growth structure and environment of the coated part and the central part is obviously different.It has experienced two growth periods,and the growth of the central part is relatively simple.The FTIR analysis indicates that the hydrogen absorption peak is lacked in coated diamonds. Quantitative analysis show that the N content of the coated part is low,and is generally much lower than the central part,speculate it is related to the rapid post-crystallization of diamond.It is obviously that the growth mechanism of coated part is different from the central part,with a shorter formation time.By inference,the center part of coated diamond forms at the early period in crystallization, begining at the bottom asthenosphere when block body rising.The diamond grew in the lithosphere which under the reduction and HTHP condition for a long time,according to the octahedron crystal habit continuously.Sequently in the rise process of Kimberley magma,the coat part crystallized fast in the unstable melt/fluid medium or the melt/fluid and kinds of captive rocks heterogeneous of mix medium.Obviously,its growth process is different from the common diamond.This is also one of manifestations about the multi-times and complex in diamond growth.