Dynamic topography of passive continental margins and their hinterlands since the Cretaceous

Abstract

Even though it is well accepted that the Earth's surface topography has been affected by mantle-convection induced dynamic topography, its magnitude and time-dependence remain controversial. The dynamic influence to topographic change along continental margins is particularly difficult to unravel, because their stratigraphic record is dominated by tectonic subsidence caused by rifting. We follow a three-fold approach to estimate dynamic topographic change along passive margins based on a set of seven global mantle convection models. We first demonstrate that a geodynamic forward model that includes adiabatic and viscous heating in addition to internal heating from radiogenic sources, and a mantle viscosity profile with a gradual increase in viscosity below the mantle transition zone, provides a greatly improved match to the spectral range of residual topography end-members as compared with previous models at very long wavelengths (spherical degrees 2-3). We then combine global sea level estimates with predicted surface dynamic topography to evaluate the match between predicted continental flooding patterns and published paleo-coastlines by comparing predicted versus geologically reconstructed land fractions and spatial overlaps of flooded regions for individual continents since 140 Ma. Modelled versus geologically reconstructed land fractions match within 10% for most models, and the spatial overlaps of inundated regions are mostly between 85% and 100% for the Cenozoic, dropping to about 75-100% in the Cretaceous. Regions that have been strongly affected by mantle plumes are generally not captured well in our models, as plumes are suppressed in most of them, and our models with dynamically evolving plumes do not replicate the location and timing of observed plume products. We categorise the evolution of modelled dynamic topography in both continental interiors and along passive margins using cluster analysis to investigate how clusters of similar dynamic topography time series are distributed spatially. A subdivision of four clusters is found to best reveal end-members of dynamic topography evolution along passive margins and their hinterlands, differentiating topographic stability, longterm pronounced subsidence, initial stability over a dynamic high followed by moderate subsidence and regions that are relatively proximal to subduction zones with varied dynamic topography histories. Along passive continental margins the most commonly observed process is a gradual motion from dynamic highs towards lows during the fragmentation of Pangea, reflecting the location of many passive margins now over slabs sinking in the lower mantle. Our best-fit model results in up to 500 (± 150) m of total dynamic subsidence of continental interiors while along passive margins the maximum predicted dynamic topographic change over 140 million years is about 350 (± 150) m of subsidence. Models with plumes exhibit clusters of transient passive margin uplift of about 200 ± 200 m, but are mainly characterised by long-term subside...

PyBacktrack 1.0: A Tool for Reconstructing Paleobathymetry on Oceanic and Continental Crust

“…The effects of dynamic topography can optionally be included in the models of tectonic subsidence (both oceanic and continental) by choosing from the currently supported dynamic topography models (M€ uller et al, 2018;Rubey et al, 2017). All models consist of a sequence of time-dependent global grids (in the mantle reference frame).…”

“…For choosing a dynamic topography model it is recommended to interactively interrogate the output of a given model on the GPlates Portal (portal.gplates.org) dynamic topography globes (M€ uller et al, 2016a), and consider the merits and potential shortcomings of models that were constructed using different boundary conditions and mantle rheologies (M€ uller et al, 2018;Rubey et al, 2017), or consider other models not currently bundled with pyBacktrack. For sites on continental crust an estimated rift start and end age should be specified in the file header.…”

“…For sites on continental crust an estimated rift start and end age should be specified in the file header. There is no single model that best captures dynamic topography in all oceanic regions, and the reader is referred to the two papers that describe the models bundled with pyBacktrack (M€ uller et al, 2018;Rubey et al, 2017). A warning message will be displayed if a dynamic topography model is selected whose starting age is younger than the oldest unit at a given site or younger than the rift initiation age supplied for a site on continental crust.…”

“…For sites on continental crust an estimated rift start and end age should be specified in the file header. For choosing a dynamic topography model it is recommended to interactively interrogate the output of a given model on the GPlates Portal (portal.gplates.org) dynamic topography globes (M€ uller et al, 2016a), and consider the merits and potential shortcomings of models that were constructed using different boundary conditions and mantle rheologies (M€ uller et al, 2018;Rubey et al, 2017), or consider other models not currently bundled with pyBacktrack. A warning message will be displayed if a dynamic topography model is selected whose starting age is younger than the oldest unit at a given site or younger than the rift initiation age supplied for a site on continental crust.…”

“…Any given geodynamic model is a greatly simplified representation of the Earth, and depends on particular initial and boundary conditions, assumptions of the rheology of the deep Earth and particular modeling philosophies and implementations. There is no single model that best captures dynamic topography in all oceanic regions, and the reader is referred to the two papers that describe the models bundled with pyBacktrack (M€ uller et al, 2018;Rubey et al, 2017). Here, we will briefly summarize how one might go about choosing a suitable model for the southwestern South Atlantic.…”