Description of Lamproite Occurrences

Abstract

Lamproites have been recognized in over 25 occurrences (provinces or fields) on all continents (Figure 3.1). In common with kimberlites, they are restricted to continental environments. As noted in Chapter 4, the formation of both kimberlite and lamproite magmas has occurred from the Precambrian to the Cenozoic, although the Mesozoic Era was the time of most frequent kimberlite emplacement, and the Cenozoic Era the most frequent lamproite formation (see Table 4.1). Although both kimberlites and lamproites exhibit intrusive and extrusive forms, lamproites are dominantly characterized by extrusive forms, whereas kimberlites mostly occur as intrusive diatremes, hypabyssal root zones, and dikes. The overall volume and number of individual intrusive or extrusive bodies of lamproite are dwarfed by those of kimberlite and other members of the mantle-derived alkaline mafic rock clan. We estimate that the total volume of known kimberlite intrusive rocks is on the order of over 5000 km³, whereas that of known lamproites is less than 100 km³. The large volume of extrusive lamproites, compared with intrusive varieties, may explain the paucity of recognized lamproites in the geological record. Once erupted, lamproite volcanic rocks are subject to rapid erosion and are rarely preserved for times in excess of 5–30 Ma. The generally younger age and shallower erosion level of lamproites compared with kimberlites can be linked to large-scale geodynamic processes: any petro-genetic model must therefore take into account these intrinsic differences in age and igneous form. A discussion of the tectonic controls on lamproite emplacement and their igneous forms can be found in Chapters 4 and 5, respectively.

These are a very unusual 101 of rocks, Prider.

Cecil E. Tilley