Inferring mantle flow histories from global continental hiatus surfaces

Vilacís Baurier, Berta (2025): Inferring mantle flow histories from global continental hiatus surfaces. Dissertation, LMU München: Fakultät für Geowissenschaften

Abstract

Mantle convection is a fundamental process that governs the evolution of our planet. The buoyancies associated with this process induce vertical deflections at the Earth's surface (i.e., dynamic topography), and flow in the asthenosphere, which can result in changes in lateral plate motion. Mapping independent geological data sets allows us to observe and track past mantle convection processes, thereby providing constraints on mantle circulation models and expanding our knowledge of the Earth's convective system over time. It is therefore important to find and map these time-dependent observations. First, oceanic spreading rates can be extracted from magnetic anomalies on the sea floor, which gives a robust history of horizontal plate motion changes. Second, dynamic topography imprints the stratigraphic record at inter-regional scales. Subsided regions result in sedimentation, while dynamically uplifted continental regions create erosional/non-depositional environments, leading to gaps in the stratigraphic record, known as sedimentary hiatus. Consequently, mapping the distribution of hiatus surfaces over time can be utilised as an independent mantle flow indicator. The present study utilises continental- and country-scale digital geological maps, with a temporal resolution of geological series (ranging from ten to tens of millions of years), to map the planform of convection through geological time. The resulting maps are the hiatus maps, which show the distribution of ``hiatus'' and ``no hiatus'' surfaces for all continents (except Antarctica) across eight geological series since the Upper Jurassic. They provide a proxy for the inter-regional patterns of uplift and subsidence associated with dynamic topography. The maps reveal that the distribution of hiatus surfaces significantly changes across and between continents at timescales of geological series. Their wavelengths are on the order of 10³ km. Some inter-regional hiatus surfaces can be linked to dynamic uplift generated by the rise of a mantle plume, as they are frequently followed by flood basalt eruptions. Furthermore, these hiatus surfaces are usually followed in the next geological series by a nearby plate motion change. Other hiatus surfaces can be linked to the transport of hot material in the asthenosphere. Moreover, sea-level variations also affect the generation of hiatus surfaces on a global scale. These variations can be distinguished from regional changes induced by dynamic topography by comparing the sediment distribution across continents. The characteristics of the hiatus maps are consistent with the presence of a mantle viscosity stratification with a weaker upper mantle and reinforce the importance of the viscosity in shaping the convective platform. The time delay between the vertical and horizontal motion of the lithosphere highlights the importance of an asthenospheric flow beneath the tectonic plates, as thermal anomalies traverse this layer and shear the base of the lithosphere. Furthermore, a change in base level of approximately \SI{100}{\meter}, whether by a sea-level variation or a dynamic topography change, affects the inter-regional sediment distribution either globally or regionally. The results of this thesis suggest that the occurrence of a hiatus surface, followed by a flood basalt eruption and subsequent horizontal plate motion change can be seen as characteristic of plume-induced dynamic uplift and asthenospheric flow. They imply that a key property of time-dependent geodynamic Earth models must be a difference in timescale between mantle convection itself and the resulting dynamic topography. Moreover, they highlight the importance of continental-scale compilations of geological data to map the temporal evolution of mantle flow beneath the lithosphere, which can provide powerful constraints for global geodynamic models.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: dynamic topography, sedimentary hiatus, mantle plume, asthenospheric flow, mantle convection, viscosity stratification
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 550 Geowissenschaften
• Fakultäten: Fakultät für Geowissenschaften
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 28. Mai 2025
• 1. Bericht­erstatter:in: Bunge, Hans-Peter