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- Title
Quantifying Diapir Ascent Velocities in Power‐Law Viscous Rock Under Far‐Field Stress: Integrating Analytical Estimates, 3D Numerical Calculations and Geodynamic Applications.
- Authors
Macherel, Emilie; Podladchikov, Yuri; Räss, Ludovic; Schmalholz, Stefan M.
- Abstract
Diapirism is crucial for heat and mass transfer in many geodynamic processes. Understanding diapir ascent velocity is vital for assessing its significance in various geodynamic settings. Although analytical estimates exist for ascent velocities of diapirs in power‐law viscous, stress weakening fluids, they lack validation through 3D numerical calculations. Here, we improve these estimates by incorporating combined linear and power‐law viscous flow and validate them using 3D numerical calculations. We focus on a weak, buoyant sphere in a stress weakening fluid subjected to far‐field horizontal simple shear. The ascent velocity depends on two stress ratios: (a) the ratio of buoyancy stress to characteristic stress, controlling the transition from linear to power‐law viscous flow, and (b) the ratio of regional stress associated with far‐field shearing to characteristic stress. Comparing analytical estimates with numerical calculations, we find analytical estimates are accurate within a factor of two. However, discrepancies arise due to the analytical assumption that deviatoric stresses around the diapir are comparable to buoyancy stresses. Numerical results reveal significantly smaller deviatoric stresses. As deviatoric stresses govern stress‐dependent, power‐law viscosity, analytical estimates tend to overestimate stress weakening. We introduce a shape factor to improve accuracy. Additionally, we determine characteristic stresses for representative mantle and lower crustal flow laws and discuss practical implications in natural diapirism, such as sediment diapirs in subduction zones, magmatic plutons or exhumation of ultra‐high‐pressure rocks. Our study enhances understanding of diapir ascent velocities and associated stress conditions, contributing to a thorough comprehension of diapiric processes in geology. Plain Language Summary: A diapir is a volume of rock that rises within a larger, denser rock mass due to its lower density and the force of gravity. Understanding the speed at which diapirs ascend is crucial for determining their significance in specific geologic settings, such as subduction zones. In this study, we use advanced computer simulations to calculate the ascent velocity of a spherical diapir within a denser surrounding material. The surrounding material is subjected to horizontal shearing, and its behavior resembles that of a nonlinear fluid, where its resistance to shear, known as viscosity, depends on the applied stress. By conducting three‐dimensional computer simulations, we not only test the accuracy of existing mathematical equations commonly used to estimate diapir velocity but also make improvements to enhance their precision. These equations help us estimate how quickly diapirs rise in different geodynamic environments. By advancing our understanding of diapir ascent velocities, we gain valuable insights into the processes that shape our planet's geological features. Key Points: 3D GPU‐based numerical calculations of diapir velocities in power‐law viscous fluid under far‐field stressNew analytical velocity estimates are controlled by two stress ratios and agree with numerical resultsStress weakening in tectonically active regions can increase diapir velocity by several orders of magnitudes
- Subjects
POWER law (Mathematics); NUMERICAL calculations; TECTONIC exhumation; VISCOUS flow; FORCE density; SUBDUCTION zones
- Publication
Geochemistry, Geophysics, Geosystems: G3, 2023, Vol 24, Issue 12, p1
- ISSN
1525-2027
- Publication type
Article
- DOI
10.1029/2023GC011115