Temporal distribution of carbonatites

About half of the 330 occurrences listed in the global inventory of carbonatites have been dated, mostly by the K-Ar method, and they fall into groups that appear to be temporally and spatially linked to major orogenic events. Overall, however, the temporal pattern is one of exponential increase in frequency with time. This secular trend has been interpreted as an increase in carbonatite activity in the course of terrestrial evolution. In an alternative interpretation, the observed trend may be viewed as an artifact of preservation, because the probability of preservation decreases exponentially with increasing age of the crustal segments. The secular trend for carbonatites since at least 1.8 Ga, the time that continental crust attained its near-modern extent, is compatible with a steady-state process of carbonatite generation and destruction that has a half-life of ∼445 m.y. The most acceptable model for the temporal distribution of carbonatites involves a combination of orogenic activity and erosional dispersal.