METAMORPHIC DECARBONATION, SILICATE WEATHERING AND THE LONG-TERM CARBON-CYCLE

The seawater Sr-87/Sr-86 curve implies a 50-100 Myr episodicity in wea thering rate which requires a corresponding variation in CO2 degassing from the solid earth to the atmosphere. It is proposed that this is c aused by orogenesis, which both produces CO2 as a result of metamorphi c decarbonation reactions, and consumes extra CO2 as a consequence of erosion-enhanced weathering. Global climate on the geological time-sca le is therefore controlled by the difference between the relatively la rge and variable orogenic-moderated degassing and weathering CO2 fluxe s.