Abstract
The fundamental advances in silicon isotope geochemistry have been systematically demonstrated in this work. Firstly, the continuous modifications in analytical approaches and the silicon isotope variations in major reservoirs and geological processes have been briefly introduced. Secondly, the silicon isotope fractionation linked to silicon complexation/coordination and thermodynamic conditions have been extensively stressed, including silicate minerals with variable structures and chemical compositions, silica precipitation and diagenesis, chemical weathering of crustal surface silicate rocks, biological uptake, global oceanic Si cycle, etc. Finally, the relevant geological implications for meteorites and planetary core formation, ore deposits formation, hydrothermal fluids activities, and silicon cycling in hydrosphere have been summarized. Compared to the thermodynamic isotope fractionation of silicon associated with high-temperature processes, that in low-temperature geological processes is much more significant (e.g., chemical weathering, biogenic/non-biogenic precipitation, biological uptake, adsorption, etc.). The equilibrium silicon isotope fractionation during the mantle-core differentiation resulted in the observed heavy isotope composition of the bulk silicate Earth (BSE). The equilibrium fractionation of silicon isotopes among silicate minerals are sensitive to the Si–O bond length, Si coordination numbers (CN), the polymerization degrees of silicate unites, and the electronegativity of cations in minerals. The preferential enrichment of different speciation of dissoluble Si (DSi) (e.g., silicic acid H4SiO40 (H4) and H3SiO4− (H3)) in silica precipitation and diagenesis, and chemical weathering, lead to predominately positive Si isotope signatures in continental surface waters, in which the dynamic fractionation of silicon isotope could be well described by the Rayleigh fractionation model. The role of complexation in biological fractionations of silicon isotopes is more complicated, likely involving several enzymatic processes and active transport proteins. The integrated understanding greatly strengthens the potential of δ30Si proxy for reconstructing the paleo terrestrial and oceanic environments, and exploring the meteorites and planetary core formation, as well as constraining ore deposits and hydrothermal fluid activity.
Highlights
As silicon is the third most abundant element on Earth (~16.1 wt.% Si) [1], the most abundant non-volatile element in the solar system after oxygen, and the second most abundant element in the upper crust (28.8 wt.%) [2], it is expected to be one of most suitable elements for understanding the fundamentals of various processes in Earth [3]
0 ka are derived based on the δ30Si measured from core samples by Horn et al (2011) [146] with the fractionation factor αdiatom–solution of 0.9985 and 0.9993, respectively; (b) evolution of seawater δ30Si recorded from Precambrian chert from 3000 Ma to 500 Ma (data compiled from Marin-Carbonnea et al (2014) [147]; (c) evolution of dissolvable Si (DSi) content in ocean responding to dominant geological event (e.g., the banded iron formation (BIF)) and biological events from the early Precambrian to the present
The fundamental advances in silicon isotope geochemistry investigations have been reviewed, including the silicon isotope fractionations linked to silicon complexations/coordination and thermodynamic conditions in various geological processes, and the geological implications for meteorites and planetary core formation, ore deposits formation and hydrothermal fluids activities, weathering rate, and silicon cycling, etc
Summary
In Boron Isotopes; Marschall, H., Foster, G., Eds.; Springer Int. Publishing: Berlin, Germany, 2018; pp. 1–11. Y.H.; Ding, T.P.; Wan, D.F. Experimental study of silicon isotope dynamic fractionation and its application in geology. S.; Vroon, P.Z.; van Bergen, M.J. Silicon isotopes and trace elements in chert record early Archean basin evolution. Silicon isotopic fractionation during adsorption of aqueous monosilicic acid onto iron oxide. L.; Hendry, K.R.; Meredith, M.P.; Venables, H.J.; De La Rocha, C.L. Silicon isotope and silicic acid uptake in surface waters of Marguerite Bay, West Antarctic Peninsula. The silicon and oxygen isotope compositions of Precambrian cherts: A record of oceanic paleo–temperatures? R.M.G.; Georg, R.B.; Williams, H.M.; Halliday, A.N. Silicon isotopes in lunar rocks: Implications for the Moon’s formation and the early history of the Earth. A.; Ziegler, K.; Young, E.D.; Ricolleau, A.; Schauble, E.A.; Fei, Y.W. Experimentally determined Si isotope fractionation between silicate and Fe metal and implications for Earth’s core formation.
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