title: Continental igneous rock composition: A major control of past global chemical weathering.
abstract: The composition of igneous rocks in the continental crust has changed throughout Earth's history. However, the impact of these compositional variations on chemical weathering, and by extension on seawater and atmosphere evolution, is largely unknown. We use the strontium isotope ratio in seawater [(87Sr/86Sr)seawater] as a proxy for chemical weathering, and we test the sensitivity of (87Sr/86Sr)seawatervariations to the strontium isotopic composition (87Sr/86Sr) in igneous rocks generated through time. We demonstrate that the87Sr/86Sr ratio in igneous rocks is correlated to the epsilon hafnium (εHf) of their hosted zircon grains, and we use the detrital zircon record to reconstruct the evolution of the87Sr/86Sr ratio in zircon-bearing igneous rocks. The reconstructed87Sr/86Sr variations in igneous rocks are strongly correlated with the (87Sr/86Sr)seawatervariations over the last 1000 million years, suggesting a direct control of the isotopic composition of silicic magmatism on (87Sr/86Sr)seawatervariations. The correlation decreases during several time periods, likely reflecting changes in the chemical weathering rate associated with paleogeographic, climatic, or tectonic events. We argue that for most of the last 1000 million years, the (87Sr/86Sr)seawatervariations are responding to changes in the isotopic composition of silicic magmatism rather than to changes in the global chemical weathering rate. We conclude that the (87Sr/86Sr)seawatervariations are of limited utility to reconstruct changes in the global chemical weathering rate in deep times.
authors.affiliation: Department of Geological Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: Clément P
authors.initials: CP
authors.lastname: Bataille
authors.affiliation: Department of Statistical Science, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Amy
authors.initials: A
authors.lastname: Willis
authors.affiliation: Department of Geological Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: Xiao
authors.identifier: 0000-0002-0046-832X
authors.initials: X
authors.lastname: Yang
authors.affiliation: Department of Geological Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: Xiao-Ming
authors.identifier: 0000-0001-7904-1056
authors.initials: XM
authors.lastname: Liu
keywords: Neoproterozoic; Paleoclimate; arcs; chemical weathering; continental crust; detrital zircon; hafnium; phanerozoic; strontium isotopes; supercontinent