Abstract
Zebra rocks, characterized by their striking reddish-brown stripes,
rods, and spots of hematite (Fe-oxide), showcase complex self-organized
patterns formed under far-from-equilibrium conditions. Despite their
recognition, the underlying mechanisms remain elusive. We introduce a
novel advection-dominated phase-field model that effectively replicates
the Liesegang-like patterns observed in Zebra rocks. This model
leverages the concept of phase separation, a well-established principle
governing Liesegang phenomena. Our findings reveal that initial solute
concentration and fluid flow velocity are critical determinants in
pattern selection and transition. We quantitatively explain the spacing
and width of a specific Liesegang-like pattern category. Furthermore,
the model demonstrates that vanishingly low initial concentrations
promote the formation of oblique patterns, with inclination angles
influenced by rock heterogeneity. Additionally, we establish a
quantitative relationship between band thickness and geological
parameters for orthogonal bands. This enables the characterization of
critical geological parameters based solely on static patterns observed
in Zebra rocks, providing valuable insights into their formation
environments. The diverse patterns in Zebra rocks share similarities
with morphologies observed on early Earth and Mars, such as banded iron
formations and hematite spherules. Our model, therefore, offers a
plausible explanation for the formation mechanisms of these patterns and
presents a powerful tool for deciphering the geochemical environments of
their origin.