| This thesis contains the results of detailed studies on diamonds and their mineral inclusions from the Panda kimberlite in Canada; from three alluvial diamond deposits in Brazil (Arenapolis, Boa Vista and Canastra); and, from the Jagersfontein kimberlite in South Africa. The results give insights into the composition and evolution of major parts of the Earth's mantle.; Incorporated are data on the physical, chemical and isotopic characteristics of the diamonds as well as data on the major-, minor- and trace-element composition of the inclusions.; The studied diamonds formed at various depths in the Earth's mantle, including the subcratonic lithospheric upper mantle (150-250 km), the asthenosphere (>250 km) and the transition zone (>410 km), and the lower mantle (>660 km). Depending on the depths of their origin, diamonds and their mineral inclusion indicate distinct chemical source environments and diamond formation processes.; The majority of lithospheric diamonds formed in a depleted peridotitic environment, which experienced an early stage of extensive melt extraction and to different degrees, subsequent re-enrichment. An overall smaller portion of diamonds formed in an eclogitic environment, which at least in some cases can be linked to subducted oceanic crust. Peridotitic and eclogitic diamond sources in the lithospheric mantle, however, are heterogeneously distributed. Diamond formation in the lithospheric mantle is in most cases related to the precipitation of CHO-rich fluids.; Unlike diamonds from the lithosphere and the lower mantle, diamonds from asthenosphere and transition zone reflect predominantly eclogitic sources. The trace-element composition of their inclusions and the carbon stable isotope characteristic of the diamond hosts indicate that these deep diamonds formed exclusively in subducting oceanic crust, most likely from graphite derived from various carbon sources within the slab. |
