Characteristics and mechanisms of multistage dolomitization in Proterozoic dolomitic breccia from agua Clara Formation, Ribeira Belt, Brazil

The Proterozoic carbonate rocks from Ribeira Belt in Rio Bonito Quarry, Southern Brazil, seem to evidence an intense hydrothermal alteration prominently indicated by three distinct dolomitization stages followed by a later dedolomitization one. This observation prompted a detailed study of the mineral phases derived of these processes, the carbonates involved in such, and the implications therein regarding the characterization of the hydrothermal dolomitization. Different phases of basinal, hydrothermal-magmatic, metamorphic and meteoric fluids were responsible by the crystallization of six distinct generations of dolomite in multistage events, which comply with different dolomitization models in literature. First, Mesoproterozoic limestones, from shallow to deep water platforms, were dolomitized (burial compaction model) by the replacement of diagenetic calcite with dolomites through the interaction of marine and basinal fluids. In pressure relief zones, the formation of the first gap-filling dolomite represented the sedimentary-metamorphic transition. During the Brasiliano-Pan African orogeny, the second dolomitization phase (tectonic model) occurred generating dolomite, inducing hydraulic fracturing and afterwards, yet another, precipitation of dolomite on the edges of fragments-thus forming a dolomitic breccia. The precipitation of the second gap-filling sample of dolomite took place simultaneously to the tectonic dolomitization phase and the hydraulic brecciation. During the third dolomitization stage (thermal convection model), hydrothermal-granitic fluids promoted the precipitation of saddle dolomite, infilling vugs. Subsequently, the dedolomitization process (thermal convection/meteoric model) ascribed to hydrothermal-granitic and meteoric fluids induced calcite, quartz, fluorite and apatite's crystallization, infilling vugs in the dolomitic breccia.

Automated summary

The Proterozoic carbonate rocks from Ribeira Belt in Rio Bonito Quarry, Southern Brazil, underwent intense hydrothermal alteration, with multiple stages of dolomitization, fracturing, and sedimentary-metamorphic transition.