Why magnesium isotope fractionation is absent from basaltic melts under thermal gradients in natural settings

Xu, Yingkui and Zhu, Dan and Li, Xiongyao and Liu, Jianzhong (2020) Why magnesium isotope fractionation is absent from basaltic melts under thermal gradients in natural settings. Geological Magazine, 157 (7). pp. 1144-1148. ISSN 14695081

Abstract

Laboratory experiments have shown that thermal gradients in silicate melts can lead to isotopic fractionation; this is known as the Richter effect. However, it is perplexing that the Richter effect has not been documented in natural samples as thermal gradients commonly exist within natural igneous systems. To resolve this discrepancy, theoretical analysis and calculations were undertaken. We found that the Richter effect, commonly seen in experiments with wholly molten silicates, cannot be applied to natural systems because natural igneous samples are more likely to be formed out of partially molten magma and the presence of minerals adds complexity to the behaviour of the isotope. In this study, we consider two related diffusion-rate kinetic isotope effects that originate from chemical diffusion, which are absent from experiments with wholly molten samples. We performed detailed calculations for magnesium isotopes, and the results indicated that the Richter effect for magnesium isotopes is buffered by kinetic isotope effects and the total value of magnesium isotope fractionation can be zero or even undetectable. Our study provides a new understanding of isotopic behaviour during the processes of cooling and solidification in natural magmatic systems.

Item Type:	Article
Identification Number:	10.1017/S0016756819001304
Uncontrolled Keywords:	Richter effect,Soret effect,magnesium isotope,thermal gradient
Depositing User:	Unnamed user with username ismiatun
Date Deposited:	11 Jun 2024 03:10
Last Modified:	11 Jun 2024 03:10
URI:	http://repository.ub.ac.id/id/eprint/220830

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