Continental-scale evolution of topography and river networks. Tectonics and climate shaping Eurasia

[This post is about our recent publication on PLOS ONE]

How much does the erosion and sedimentation at the Earth’s surface influence on the patterns and distribution of tectonic deformation? This question has been mainly addressed from a computer modelling perspective, at scales ranging from local to orogenic. In the PLOS ONE paper published today, we present a model that aims at understanding this phenomenon at the continental scale, looking at the feedbacks between continental enlargement and climate aridification during the collision of continents.

60-million-year indentation of a continent from the south 

(at 50 mm/yr). 

Left: Topography and areas with precipitation
higher than 400 mm/yr (red shading). Note the 

orographic rainfall developing at the southern flank 

of the growing plateau. Wind blows from the southeast 

(towards the upper left corner).

Right: erosion and sedimentation rates, and
contours of crustal thickening rate due to tectonics. 

By Garcia-Castellanos & Jimenez-Munt, PLOS ONE, 2015. 

+ info here.

We couple a thin-sheet viscous model of continental deformation with a stream-power surface transport model. The model also incorporates flexural isostatic compensation that permits the formation of large sedimentary basins and a precipitation model that reproduces basic climatic effects such as continentality and orographic rainfall and rain shadow. We calculate the feedbacks between these four processes acting at different scales in a synthetic scenario inspired and scaled by the India-Asia collision. The model reproduces first-order characteristics of the growth of the Tibetan Plateau as a result of the Indian indentation.

Note that the southern continent (the indenter, India)
is chosen fixed to our reference frame, whereas
 the northern continent (Asia) is moving southwards). 

The initial topography is flat with small random noise
forming a network of lakes. The tectonic indenter in
the southern boundary represents India, while a rigid
block fixed around x=2500km represents the Tarim Basin. 

Wind blowing from SE at 7 m/s (relative humidity=1).
Red shading indicates orographic precipitation.

The continental deformation adopts a thin-sheet tectonic
model. + info here.

What these simulations show is that, at large space and temporal scales, the climate dryness that develops in continental interiors triggers the trapping of sediment in closed basins within the continent, instead of exporting it to the continental margins. In the left panel you can see a large intramountain basin (comparable to the Tarim Basin) developing within Asia when a hard lithospheric region in predefined within the continent. The amount of sediment trapped in it is very sensitive to climatic parameters, particularly to evaporation, because it crucially determines its endorheic/exorheic drainage. We identify a feedback between erosion and crustal thickening leading locally to a <50 at="" climatically-enhanced="" concentrated.="" corners="" deformation="" flank="" growing="" in="" increase="" indenter="" is="" of="" orographic="" p="" place="" places="" plateau="" precipitation="" preferentially="" rates="" specially="" syntaxes="" takes="" the="" this="" upwind="" where="">

We hypothesize that this may provide clues for better understanding the mechanisms underlying the intriguing tectonic aneurysms documented in the Himalayas. At the continental scale, however, the overall distribution of topographic basins and ranges

seems insensitive to climatic factors, despite these do have important, sometimes counterintuitive effects on the amount of sediments trapped within the continent. The dry climatic conditions that naturally develop in the interior of the continent, for example, trigger large intra-continental sediment trapping at basins similar to the Tarim Basin because they determine its endorheic/exorheic drainage. These complex climatic-drainage-

tectonic interactions make the development of steady-state topography at the continental scale unlikely.