Do olivine crystallization temperatures faithfully record mantle temperature variability?

Matthews, Wong, Shorttle, Edmonds, Maclennan, G3 (2021). doi: 10.1029/2020GC009157

Mantle temperatures are thought to vary substantially in the present day throughout the Earth, as a consequence of the vigorous convective cycling within our planet’s interior. Additionally, mantle temperatures are thought to vary through time. Estimating mantle temperatures in the ancient Earth can be more complex than for the present day Earth. In many cases the constraints we would like to use have to be indirectly inferred for the Earth’s past.

However, petrological techniques can be applied equally to both modern and ancient volcanic rocks. The temperature at which a magma starts crystallising is determined in large part by the temperature of the mantle whence it derived. Mantle composition also exerts a control (which we explored for Iceland in Matthews et al., 2016). In this new contribution we assess to what extent crystallisation temperatures can be relied on as a proxy for mantle temperature in the absence of information about mantle composition.

Central to our methods is an open source python module that we have developed for calculating mantle melting behaviour- pyMelt. To use the model without installing the python module, see our web-based app: pymelt.swmatthews.com.

The image is from the Supplementary Information for the manuscript. It shows how we can use an electron probe to map the aluminium contents of olivine crystals. By measuring the aluminium content of coexisting olivine and spinel we can estimate the temperature they crystallised from magma.

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