Rock Chemistry Tectonics and the Carbon Sink

Another recent theory regarding the relationship of tectonics to climate deserves mention. Reusch and Maasch (1995) proposed that the uplift and weathering of magmatic arcs rich in mafic rocks have intensified the carbon sink with respect to the atmosphere. This enhancement is plausible because mafic rocks are richer in CaMg silicates, particularly those that react fastest with soil acids (e.g., olivine, calcium-rich plagioclase). A prominent example in the Cenozoic is New Guinea, with abundant ophiolites, situated in a tropical weathering regime. They estimate an enhancement of 8.6 times in the weathering rate of simatic crust (mafic and ultramafic rocks rich in calcium and magnesium) relative to sialic crust (rich in silicon) (Reusch and Maasch 1995). However, one study on chemical weathering rates in tropical areas has indicated a more modest enhancement for the case of basalt relative to acidic volcanic rocks (Amiotte Suchet and Probst 1993). Reusch and Maasch's hypothesis is currently under discussion. The Cenozoic record of oxygen, strontium, and osmium isotopes does not appear to support their proposal for the role of New Guinea (Caldeira, personal communication). Nevertheless, the role of rock chemistry in the codetermination of the carbon sink along with climate and biota is likely important and merits further study.

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