Carbonatite

Carbonatite

Carbonatites ( /kɑrˈbɒnətaɪt/) are intrusive or extrusive igneous rocks defined by mineralogic composition consisting of greater than 50 percent carbonate minerals. Carbonatites may be confused with marble, and may require geochemical verification.

Carbonatites usually occur as small plugs within zoned alkalic intrusive complexes, or as dikes, sills, breccias, and veins. They are, almost exclusively, associated with continental rift-related tectonic settings. The majority of carbonatites are Proterozoic or Phanerozoic in age. It seems that there has been a steady increase in the carbonatitic igneous activity through the earth's history, from the Archean Eon to the present.

Nearly all carbonatite occurrences are intrusives or subvolcanic intrusives. This is because carbonatite lava flows are unstable and react quickly in the atmosphere. Carbonatite lavas may not be as uncommon as thought, but have been poorly preserved throughout earth's history.

Only one carbonatite volcano is known to have erupted in historical time, the active Ol Doinyo Lengai volcano in Tanzania. It erupts with the lowest temperature lava in the world, at 500-600 °C. The lava is natrocarbonatite dominated by nyerereite and gregoryite.