Abstract
The linear carbonatites from mobile belts are located in fault zones, extend over scores of kilometers, are not directly associated with igneous alkaline rocks, but are surrounded by wide zoned aureoles of alkaline metasomatites (fenites). They are conformable with the altitude of the host rocks, and run parallel to the overall orientation of the mobile belt; intrusion of the carbonatite bodies occurs prior to stabilization of the mobile belt and precedes the orogenic phase. The carbonatite bodies occur in current mobile belts, folded belts of Neogen, and in analogous formations from the Paleozoic and Proterozoic ages. They show comparatively simple mineral composition, single-petrographic facies, single-stage of intrusion, clear vertical differentiation, characterized by three distinct intrusion facies of carbonatites, according to the depth of emplacement in relation to the paleorelief: shallow depth facies (2-5 km, T< 400°C, P <1,5 kbar); middle depth (5-10 km, T= 400-600°, P= 1,5 - 3,0 kbar) and great depth (> 10 km, T >600° C, P >3 kbar). Each of the fácies is cohstituted by a proper assemblage of tipomorphic rock and ore forming minerais. To exemplify, we describe the general features of the two linear carbonatites most studied abroad, as well as the only one of its type known in Brazil to date.
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