Global geologic and geomorphic observations of mantle convection

This presentation examines how the growing inventory of geologic, geophysical and geomorphic observations constrains amplitudes, wavelengths and histories of mantle convection. Ocean age-depth residuals have become a cornerstone in understanding loci, amplitudes and wavelengths of modern sub-plate support of Earth’s oceanic lithosphere. Improvements in mapping lithospheric structure, especially from seismology, means that quantifying modern sub-plate support of continents is increasingly tractable. The continents offer a great opportunity to constrain temporal and spatial evolution of sup-plate support because of the plethora of available geologic and geomorphic observations. A challenge is to disentangle, often dominant, lithospheric processes that generate uplift or subsidence (e.g. shortening, extension) to extract information about histories of sub-plate processes from geologic and geomorphic observations. This presentation focusses on how data and theory can be combined to quantify [1] modern and recent sub-plate support of the continents, [2] evolution of sub-plate support through time, and [3] test geodynamic models that predict dynamic topography.

 

Highlights from recent work include the use of collocated long wavelength gravity and shear wave velocity anomalies, mafic magmatism and drainage patterns to identify tracts of uplifted continental topography that are maintained by sub-plate support. These observations indicate that chemical and sedimentary fluxes through drainage networks are likely governed by sub-plate support in many places. Observational and theoretical constraints on uplift and subsidence histories of continents and their margins are presented. These include global paleobiological observations of uplifted marine rock, backstripped stratigraphy (e.g. New Jersey margin, Mauritanian basin), inversion of drainage patterns (e.g. North America, Africa) and landscape evolution modelling. This work indicates that re-assessment of the longevity and evolution of Earth’s surface topography, basin formation and histories of glacio-eustasy is required. Reasons for why large-scale vertical lithospheric motions, often associated with dynamic support, are likely to be recorded in modern and ancient continental landscapes are explored using spectral analysis of drainage patterns and physics-based modelling of erosional thresholds. Examples of how seismology, anelastic parameterisations, thermobarometry, geodesy, stratigraphy and geomorphic observations can be reconciled to constrain Cenozoic to Recent histories of upper mantle support are presented. Finally, examples of using geologic observations to test predictions from geodynamic models are given. Opportunities and challenges associated with assessing contributions of sub-plate support to evolution of Earth’s surface, particularly those associated with crust and lithospheric mantle densities, are discussed. Available observations show that Cenozoic mantle convection has been a significant, in places dominant, driver of continental evolution. It has generated and maintains epicontinental seaways, sedimentary basins, continental plateaux, and has determined routing of water and sediment across continents and biodiversity. It is an important driver of Earth surface evolution and is extremely likely to have left its trace throughout the geologic and geomorphic record.