Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Journal of Geophysical Research - Solid Earth. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing the latest version by default [v1]Anisotropy and microcrack propagation induced by weathering, regional stresses and topographic stressesAuthorsTingtingXuXiandaShenMilesReedNicoleWestKenFerrieriDChloéArsoniDSee all authors Tingting XuGeorgia Institute of Technologyview email addressThe email was not providedcopy email addressXianda ShenClarkson Universityview email addressThe email was not providedcopy email addressMiles ReedUniversity of Wisconsin-Madisonview email addressThe email was not providedcopy email addressNicole WestCentral Michigan Universityview email addressThe email was not providedcopy email addressKen FerrieriDUniversity of Wisconsin-MadisoniDhttps://orcid.org/0000-0003-4098-166Xview email addressThe email was not providedcopy email addressChloé ArsoniDCorresponding Author• Submitting AuthorGeorgia Institute of TechnologyiDhttps://orcid.org/0000-0002-4477-1072view email addressThe email was not providedcopy email address
Abstract This paper presents a new model for anisotropic damage in bedrock under the combined influences of biotite weathering, regional stresses, and topographic stresses. We used the homogenization theory to calculate the mechanical properties of a rock representative elementary volume made of a homogeneous matrix, biotite inclusions that expand as they weather, and ellipsoidal cracks of various orientations. With this model, we conducted a series of finite element simulations in bedrock under gently rolling topography with two contrasting spatial patterns in biotite weathering rate and a range of biotite orientations. In all simulations, damage is far more sensitive to biotite weathering than to topographic or regional stresses. The spatial gradient of damage follows that of the imposed biotite weathering rate at all times. The direction of micro‐cracks tends to align with that of the biotite minerals. Relative to the topographic and regional stresses imparted by the boundary conditions of the model, the stress field after 1,000 years of biotite weathering exhibits higher magnitudes, wider shear stress zones at the feet of hills, more tensile vertical stress below the hilltops, and more compressive horizontal stress concentrated in the valleys. These behaviors are similar in simulations of slowing eroding topography and static topography. Over longer periods of time (500 kyr), the combined effects or weathering and erosion result in horizontal tensile stress under the hills and vertical tensile stress under and in the hills. These simulations illustrate how this model can help elucidate the influence of mineral weathering on Critical Zone evolution.
Abstract Terrestrial cosmogenic nuclides (TCN) are widely employed to infer denudation rates in mountainous landscapes. The calculation of an inferred denudation rate ( D inf ) from TCN concentrations is typically performed under the assumptions that denudation rates were steady during TCN accumulation and that soil chemical weathering negligibly impacted soil mineral abundances. In many landscapes, however, denudation rates were not steady and soil composition was significantly impacted by chemical weathering, which complicates interpretation of TCN concentrations. We present a landscape evolution model that computes transient changes in topography, soil thickness, soil mineralogy, and soil TCN concentrations. We used this model to investigate TCN responses in transient landscapes by imposing idealized perturbations in tectonically (rock uplift rate) and climatically sensitive parameters (soil production efficiency, hillslope transport efficiency, and mineral dissolution rate) on initially steady‐state landscapes. These experiments revealed key insights about TCN responses in transient landscapes. (a) Accounting for soil chemical erosion is necessary to accurately calculate D inf . (b) Responses of D inf to tectonic perturbations differ from those to climatic perturbations, suggesting that spatial and temporal patterns in D inf are signatures of perturbation type and magnitude. (c) If soil chemical erosion is accounted for, basin‐averaged D inf inferred from TCN in stream sediment closely tracks actual basin‐averaged denudation rate, showing that D inf is a reasonable proxy for actual denudation rate, even in many transient landscapes. (d) Response times of D inf to perturbations increase with hillslope length, implying that response times should be sensitive to the climatic, biological, and lithologic processes that control hillslope length.
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