FTIR mapping of diamond plates of eclogitic and peridotitic xenoliths from the Nyurbinskaya pipe, Yakutia: genetic implications

Results of studies of IR absorption and photo- and cathodoluminescence of diamonds from peridotitic and eclogitic xenoliths from the Nyurbinskaya pipe are presented. The internal structure of diamonds of different genesis and the changes in their impurity composition throughout the crystals are analyzed. A comparison is made for the spectral parameters of crystals from xenoliths of different genesis and from kimberlites of this pipe. The internal structure of 38 eclogitic and 4 peridotitic diamond (class -4 to + 2 mm) crystals is examined on their 0.4-0.8 mm thick plane-parallel plates. We present results of a detailed study of diamonds with different characteristics from four eclogitic and two peridotitic xenoliths from the Nyurbinskaya pipe. Areal mapping of diamond plates from xenoliths showed varying contents of total nitrogen, its aggregates, and hydrogen and their zonal distribution in the investigated crystals. Peridotitic diamonds are characterized by low and medium nitrogen contents, a high degree of nitrogen aggregation, and low contents of hydrogen and seldom show signs of growth interruption. Eclogitic diamonds have high contents of nitrogen and hydrogen; there are many zoned diamonds with signs of multistage growth among them, which indicates that they are of several growth generations. The composition of inclusions, the distribution of nitrogen impurity, and the degree of nitrogen aggregation in diamonds testify to a predominance of eclogitic paragenesis crystals in the Nyurbinskaya pipe. The internal structure of eclogitic paragenesis crystals, the arrangement of diamonds in eclogitic xenoliths, and other facts argue for their later, compared with peridotitic xenolith diamonds, formation from fluid or fluid-melt during metasomatism. This determined the typomorphism of diamonds and high productivity of the pipe.