Reliability of detrital marine sediments as proxy for continental crust composition: The effects of hydrodynamic sorting on Ti and Zr isotope systematics

The isotopic composition of the detrital sediment record harbours a valuable proxy for estimating erodible upper crust since Archaean. Refractory elements such as titanium (Ti) and zirconium (Zr) can display systematic variations in their result magmatic differentiation. Hence, sediments could potentially be used to infer average (e.g., SiO2 content) source region, even when elemental systematics are obfuscated by weathering diagenetic processes. A key premise this approach is that remains unbiased relative protolith. To what extent fractionation occur during sedimentary processes, notably hydrodynamic sorting heavy mineral assemblages with contrasting compositions, poorly understood. We investigate effects processes on Ti Zr isotope suite from Eastern Mediterranean Sea (EMS). These binary mixtures two main provenance components, Saharan dust Nile sediment, strongly mineralogical geochemical signatures. EMS clear evidence zircon, expressed large variation Zr/Al2O3 deviation εHf terrestrial εNd-εHf array. Our new data, however, do not show pronounced resulting either zircon or provenance. Although agrees theoretical models predict negligible equilibrium zircon-melt fractionation, it contrasts recent observations suggesting kinetic might common feature igneous rocks. For sediments, shift through means fine-grained samples accurately reflect source. nearly overlapping compositions Sahara- Nile-derived mean isotopes, case, have insufficient resolution useful proxy. Titanium behaves differently. small but resolvable, difference observed between Sahara components. Samples strong signature some oxides tandem much stronger effect inferred sediment. Regression shows component fractionated compared its protolith, Ethiopian flood basalts. Whereas carried essentially unmodified concentration, inference composition, sources delta, large-scale Fe-Ti occurs littoral cell. This process causes decrease TiO2/Al2O3 residual fraction shifts heavier compositions. potential an “oxide effect” has implications crustal evolution use isotopes proportion felsic account scatter shale record.