Gülcher, AJP;
Gebhardt, DJ;
Ballmer, MD;
Tackley, PJ;
(2020)
Variable dynamic styles of primordial heterogeneity preservation in the Earth's lower mantle.
Earth and Planetary Science Letters
, 536
, Article 116160. 10.1016/j.epsl.2020.116160.
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Abstract
The evolution of the system Earth is critically influenced by the long-term dynamics, composition and structure of the mantle. While cosmochemical and geochemical constraints indicate that the lower mantle hosts an ancient primordial reservoir that may be enriched in SiO2 with respect to the upper mantle, geophysical observations and models point to efficient mass transfer and convective mixing across the entire mantle. Recent hypotheses of primordial-material preservation in a convecting mantle involve delayed mixing of intrinsically dense and/or intrinsically strong heterogeneity. Yet, the effects of composition-dependent rheology and density upon heterogeneity preservation and the dynamics of mantle mixing remain poorly understood. Here, we present two-dimensional numerical models in spherical geometry, investigating the preservation styles of primordial material as a function of its physical properties (i.e., viscosity and density contrasts). We establish multiple regimes of primordial-material preservation that can occur in terrestrial planets. These include (1) efficient mixing, (2) double-layered convection with or without topography, and (3) variable styles of partial heterogeneity preservation (e.g., as diffuse domains, piles or viscous blobs in the lower mantle). Some of these regimes are here characterised for the first time, and all regimes are put into context with each other as a function of model parameters. The viscous-blobs and diffuse-domains regimes can reconcile the preservation of primordial domains in a convecting mantle, potentially resolving the discrepancy between geochemical and geophysical constraints for planet Earth. Several, if not all, regimes characterised here may be relevant to understand the long-term evolution of terrestrial planets in general.
| Type: | Article |
|---|---|
| Title: | Variable dynamic styles of primordial heterogeneity preservation in the Earth's lower mantle |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1016/j.epsl.2020.116160 |
| Publisher version: | https://doi.org/10.1016/j.epsl.2020.116160 |
| Language: | English |
| Additional information: | This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions. |
| Keywords: | Earth structure, compositional heterogeneity, mantle dynamics, primordial domains, mantle composition, primitive material |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10093535 |
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