Nitrogen distribution in diamonds from the kimberlite pipe No.50 at Fuxianin eastern China: A CL and FTIR study

CL (cathodoluminescence) and FTIR (Fourier Transform Infrared) techniques h ave been used to study internal structure, variations of N abundance and ag gregation states of diamonds collected from kimberlite pipe No.50, Fuxian, Liaoning province, China. Three kinds of internal structures can be recogni zed: (1) single stage of growth structure, (2) multi-stage of complex growt h structure, and (3) rare agate-like structure. Most of diamonds exhibit co mplex growth histories recording processes in the lithosphere over the resi dence time of diamond. Three diamonds were cut and polished parallel to (11 0). Diamonds with bright blue CL have higher N contents whereas dark green or green-blue CL duplicated oscillatory zone has moderate N content. The ag gregation states and nitrogen data across the plate indicate that the diamo nd Lc35 (0.26 ct., 3.2x3.6 mm) experienced at least four growth stages. Two resorptions and one abrupt were occurred between four stages. N content va ries from 679 to 244 atom ppm in this diamond. The variation of N contents is irregularly from core to rirn, and it is individuals within single growt h stage. N concentrations decrease form earlier to later growth in third an d fourth stages respectively. The sharp increase of N contents have been fo und at the boundaries between second and third stages and decrease at third and forth stages indicating the different environments occurred during cry stallized period of diamond. In the earlier period (may be before 1.3 to IA Ga) the environment was relative unstable with rapid growth rate of diamond , whereas in the later period (after 1.3 to 1.4Ga) the environment was stab le with slower growth rate of diamonds and enhanced fluid activity. The res ults of calculated t(MR) supported the longevity of diamonds over than a th ousand million years at mantle lithosphere. (C) 2001 Elsevier Science Ltd. All rights reserved.