Browsing by Author "Liu, Boda"

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    Thick crust, hydrous magmas, and the paradox of voluminous cold magmatism
    (Presses universitaires de Strasbourg, 2021) Lee, Cin-Ty; Liu, Boda; Earth, Environmental and Planetary Sciences
    Andesites are refined and “cold” magmas compared to their basaltic parents, yet large volumes of andesites are generated at continental arcs. We show that large andesitic plutons are favored when arc crust attains a thickness of ~60 km while mafic plutons are small and favored when arc crust is thin. Using simple thermal models, we show that large, long-lived and relatively cold partially molten zones, sustained by recharge of hydrous basaltic magmas, are favored at depth when arc crust is thick due to the reduced efficiency of heat loss with increasing crustal thickness. Thin crust and drier magmas favor hotter and thinner partially molten zones. Our study provides an explanation for the apparent paradox that the most voluminous magmas in continental arc settings are cold. The origin of andesites may be linked to the interplay between magmatic differentiation, the availability of water, and the processes that control crustal thickness.
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    Widespread phosphorous excess in olivine, rapid crystal growth, and implications for magma dynamics
    (Presses universitaires de Strasbourg, 2022) Lee, Cin-Ty; Sun, Chenguang; Sharton-Bierig, Eytan; Phelps, Patrick; Borchardt, Jackson; Liu, Boda; Costin, Gelu; Johnston, A. Dana; Earth, Environmental and Planetary Sciences
    Trace element zoning is often used to unravel the crystallization history of phenocrysts in magmatic systems, but interpretation requires quantifying the relative importance of equilibrium versus disequilibrium. Published partition coefficients for phosphorous (P) in olivine vary by more than a factor of ten. After considering kinetic effects, a new equilibrium partition coefficient was extrapolated from a re-examination of natural and experimental systems, indicating that P partition coefficients in olivine are significantly over-estimated. These new partitioning constraints allow us to establish a theoretical P Equilibrium Fractionation Array (PEFA) for mid-ocean ridge basalts (MORBs), revealing that most olivines from MORBs have excess P (2–15 times PEFA) and are thus in disequilibrium. Using an independent case study of natural dendritic olivines, we show that such P enrichments can be explained by diffusion-limited incorporation of P during rapid crystal growth. If growth rate can be related to cooling, the rapid growth rates of olivines have implications for magma system dynamics, such as the size of magma bodies or where crystallization occurs within the body.