Nitrogen-defect aggregation characteristics of some Australasian diamonds: time-temperature constraints on the source regions of pipe and alluvial diamonds

The proportion of aggregated N substitutional defects, platelet intensities, and bulk N contents have been quantitatively determined in type Ia diamonds from the Argyle and Ellendale olivine lamproite pipes (Kimberley block of northwest Australia) and alluvial deposits in western and central Kalimantan (Indonesia) and Copeton (eastern Australia) using Fourier transform infrared (FTIR) microscopy. The results show that the Ellendale eclogitic diamonds were resident in cool lithosphere and have not experienced the higher temperatures typical of Argyle diamonds. Constraints from inclusion geothermometry indicate that Ellendale eclogitic diamonds must be younger than Argyle diamonds, and a Phanerozoic age is suggested. -from Authors