Peridotite weathering is the missing ingredient of Earth’s continental crust composition

Abstract

The chemical composition of the continental crust cannot be adequately explained by current models for its formation, because it is too rich in Ni and Cr compared to that which can be generated by any of the proposed mechanisms. Estimates of the crust composition are derived from average sediment, while crustal growth is ascribed to amalgamation of differentiated magmatic rocks at continental margins. Here we show that chemical weathering of Ni- and Cr-rich, undifferentiated ultramafic rock equivalent to ~1.3 wt% of today’s continental crust compensates for low Ni and Cr in formation models of the continental crust. Ultramafic rock weathering produces a residual that is enriched in Ni and also silica. In the light of potentially large volumes of ultramafic rock and high atmospheric CO2 concentrations during the Archean, chemical weathering must therefore have played a major role in forming compositionally evolved components of the early Earth’s crust.

Solubility of the hydrated Mg-carbonates nesquehonite and dypingite from 5 to 35 °C: Implications for CO2 storage and the relative stability of Mg-carbonates

“…Ultramafic rock such as serpentinite contributes disproportionately to the release of chromium globally during natural weathering processes compared to other rock-types, owing to its high reactivity and high chromium content (McClain and Maher, 2016;Beinlich et al, 2018). It has recently been observed that secondary Mg-carbonate minerals formed during the weathering of ultramafic rock can help to mitigate the release of metals such as chromium, due both to incorporation of the metals into the carbonate minerals, and trapping of particulates within carbonate cement (Hamilton et al, 2016;Hamilton et al, 2018).…”

Reliable electrochemical phase diagrams of magnetic transition metals and related compounds from high-throughput ab initio calculations

“…During the longterm geological evolution of ultramafic rocks driven by aqueous fluid, magnetite (Fe 3 O 4 ) rather than hematite (Fe 2 O 3 ) minerals formed from primary olivine minerals. 77 It should be the electrochemically stable Fe 3 O 4 in iron ore (i.e., lodestone, a magnetite mineral) that is pervasive. Indeed, magnetite nanocrystals have also been widely found in magnetotactic bacteria 78,79 and under the upper-beak skin of homing pigeons.…”

Consumption of Atmospheric Carbon Dioxide through Weathering of Ultramafic Rocks in the Voltri Massif (Italy): Quantification of the Process and Global Implications

“…Chemical weathering of ultramafic rocks is one of the most important sinks for atmospheric CO 2 over geologic time [33,34]. Weathering rates and carbon dioxide consumption are linked to a complex combination of lithology, runoff, and temperature, and it is difficult to isolate the effects of each single variable on a global scale.…”

“…The weathering process transforms CO 2 into bicarbonate, that in the long term (time > 1 Ma) precipitates as Ca and Mg carbonate in the oceans. Ultramafic rocks, almost completely composed by Mg, Fe, and Ca silicates, are the rocks with the highest potential for the removal of CO 2 from the atmosphere-hydrosphere system and their alteration process significantly affected the evolution of the Earth's atmosphere [33] and continental crust through geological times [34]. Despite the interest on ultramafic rocks for their potential use in the field of mineral carbonation [35,36] and their importance for the study of the atmospheric evolution, the rate of CO 2 uptake via weathering of peridotite and serpentinite is still poorly known in natural conditions [37].…”